diff --git a/pytorch_lightning/metrics/__init__.py b/pytorch_lightning/metrics/__init__.py
index 53f6b5b..68268c6 100644
--- a/pytorch_lightning/metrics/__init__.py
+++ b/pytorch_lightning/metrics/__init__.py
@@ -34,4 +34,5 @@ from pytorch_lightning.metrics.regression import (  # noqa: F401
     ExplainedVariance,
     PSNR,
     SSIM,
+    R2Score
 )
diff --git a/pytorch_lightning/metrics/functional/__init__.py b/pytorch_lightning/metrics/functional/__init__.py
index 3aa5335..b4cd125 100644
--- a/pytorch_lightning/metrics/functional/__init__.py
+++ b/pytorch_lightning/metrics/functional/__init__.py
@@ -28,9 +28,9 @@ from pytorch_lightning.metrics.functional.classification import (  # noqa: F401
     to_categorical,
     to_onehot,
 )
-from pytorch_lightning.metrics.functional.confusion_matrix import confusion_matrix  # noqa: F401
 # TODO: unify metrics between class and functional, add below
 from pytorch_lightning.metrics.functional.accuracy import accuracy  # noqa: F401
+from pytorch_lightning.metrics.functional.confusion_matrix import confusion_matrix  # noqa: F401
 from pytorch_lightning.metrics.functional.explained_variance import explained_variance  # noqa: F401
 from pytorch_lightning.metrics.functional.f_beta import fbeta, f1  # noqa: F401
 from pytorch_lightning.metrics.functional.hamming_distance import hamming_distance  # noqa: F401
@@ -40,6 +40,7 @@ from pytorch_lightning.metrics.functional.mean_squared_log_error import mean_squ
 from pytorch_lightning.metrics.functional.nlp import bleu_score  # noqa: F401
 from pytorch_lightning.metrics.functional.precision_recall_curve import precision_recall_curve  # noqa: F401
 from pytorch_lightning.metrics.functional.psnr import psnr  # noqa: F401
+from pytorch_lightning.metrics.functional.r2score import r2score  # noqa: F401
 from pytorch_lightning.metrics.functional.roc import roc  # noqa: F401
 from pytorch_lightning.metrics.functional.self_supervised import embedding_similarity  # noqa: F401
 from pytorch_lightning.metrics.functional.ssim import ssim  # noqa: F401
diff --git a/pytorch_lightning/metrics/functional/r2score.py b/pytorch_lightning/metrics/functional/r2score.py
new file mode 100644
index 0000000..f689e3a
--- /dev/null
+++ b/pytorch_lightning/metrics/functional/r2score.py
@@ -0,0 +1,126 @@
+# Copyright The PyTorch Lightning team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from typing import Tuple
+
+import torch
+
+from pytorch_lightning.metrics.utils import _check_same_shape
+from pytorch_lightning.utilities import rank_zero_warn
+
+
+def _r2score_update(
+        preds: torch.tensor,
+        target: torch.Tensor,
+) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor, torch.Tensor]:
+    _check_same_shape(preds, target)
+    if preds.ndim > 2:
+        raise ValueError('Expected both prediction and target to be 1D or 2D tensors,'
+                         f' but recevied tensors with dimension {preds.shape}')
+    if len(preds) < 2:
+        raise ValueError('Needs atleast two samples to calculate r2 score.')
+
+    sum_error = torch.sum(target, dim=0)
+    sum_squared_error = torch.sum(torch.pow(target, 2.0), dim=0)
+    residual = torch.sum(torch.pow(target - preds, 2.0), dim=0)
+    total = target.size(0)
+
+    return sum_squared_error, sum_error, residual, total
+
+
+def _r2score_compute(sum_squared_error: torch.Tensor,
+                     sum_error: torch.Tensor,
+                     residual: torch.Tensor,
+                     total: torch.Tensor,
+                     adjusted: int = 0,
+                     multioutput: str = "uniform_average") -> torch.Tensor:
+    mean_error = sum_error / total
+    diff = sum_squared_error - sum_error * mean_error
+    raw_scores = 1 - (residual / diff)
+
+    if multioutput == "raw_values":
+        r2score = raw_scores
+    elif multioutput == "uniform_average":
+        r2score = torch.mean(raw_scores)
+    elif multioutput == "variance_weighted":
+        diff_sum = torch.sum(diff)
+        r2score = torch.sum(diff / diff_sum * raw_scores)
+    else:
+        raise ValueError('Argument `multioutput` must be either `raw_values`,'
+                         f' `uniform_average` or `variance_weighted`. Received {multioutput}.')
+
+    if adjusted < 0 or not isinstance(adjusted, int):
+        raise ValueError('`adjusted` parameter should be an integer larger or'
+                         ' equal to 0.')
+
+    if adjusted != 0:
+        if adjusted > total - 1:
+            rank_zero_warn("More independent regressions than datapoints in"
+                           " adjusted r2 score. Falls back to standard r2 score.",
+                           UserWarning)
+        elif adjusted == total - 1:
+            rank_zero_warn("Division by zero in adjusted r2 score. Falls back to"
+                           " standard r2 score.", UserWarning)
+        else:
+            r2score = 1 - (1 - r2score) * (total - 1) / (total - adjusted - 1)
+    return r2score
+
+
+def r2score(
+        preds: torch.Tensor,
+        target: torch.Tensor,
+        adjusted: int = 0,
+        multioutput: str = "uniform_average",
+) -> torch.Tensor:
+    r"""
+    Computes r2 score also known as `coefficient of determination
+    <https://en.wikipedia.org/wiki/Coefficient_of_determination>`_:
+
+    .. math:: R^2 = 1 - \frac{SS_res}{SS_tot}
+
+    where :math:`SS_res=\sum_i (y_i - f(x_i))^2` is the sum of residual squares, and
+    :math:`SS_tot=\sum_i (y_i - \bar{y})^2` is total sum of squares. Can also calculate
+    adjusted r2 score given by
+
+    .. math:: R^2_adj = 1 - \frac{(1-R^2)(n-1)}{n-k-1}
+
+    where the parameter :math:`k` (the number of independent regressors) should
+    be provided as the ``adjusted`` argument.
+
+    Args:
+        pred: estimated labels
+        target: ground truth labels
+        adjusted: number of independent regressors for calculating adjusted r2 score.
+            Default 0 (standard r2 score).
+        multioutput: Defines aggregation in the case of multiple output scores. Can be one
+            of the following strings (default is ``'uniform_average'``.):
+
+            * ``'raw_values'`` returns full set of scores
+            * ``'uniform_average'`` scores are uniformly averaged
+            * ``'variance_weighted'`` scores are weighted by their individual variances
+
+    Example:
+
+        >>> from pytorch_lightning.metrics.functional import r2score
+        >>> target = torch.tensor([3, -0.5, 2, 7])
+        >>> preds = torch.tensor([2.5, 0.0, 2, 8])
+        >>> r2score(preds, target)
+        tensor(0.9486)
+
+        >>> target = torch.tensor([[0.5, 1], [-1, 1], [7, -6]])
+        >>> preds = torch.tensor([[0, 2], [-1, 2], [8, -5]])
+        >>> r2score(preds, target, multioutput='raw_values')
+        tensor([0.9654, 0.9082])
+    """
+    sum_squared_error, sum_error, residual, total = _r2score_update(preds, target)
+    return _r2score_compute(sum_squared_error, sum_error, residual, total, adjusted, multioutput)
diff --git a/pytorch_lightning/metrics/regression/__init__.py b/pytorch_lightning/metrics/regression/__init__.py
index 8f48189..3e2fed1 100644
--- a/pytorch_lightning/metrics/regression/__init__.py
+++ b/pytorch_lightning/metrics/regression/__init__.py
@@ -17,3 +17,4 @@ from pytorch_lightning.metrics.regression.mean_squared_log_error import MeanSqua
 from pytorch_lightning.metrics.regression.explained_variance import ExplainedVariance  # noqa: F401
 from pytorch_lightning.metrics.regression.psnr import PSNR  # noqa: F401
 from pytorch_lightning.metrics.regression.ssim import SSIM  # noqa: F401
+from pytorch_lightning.metrics.regression.r2score import R2Score  # noqa: F401
diff --git a/pytorch_lightning/metrics/regression/r2score.py b/pytorch_lightning/metrics/regression/r2score.py
new file mode 100644
index 0000000..f8f6e98
--- /dev/null
+++ b/pytorch_lightning/metrics/regression/r2score.py
@@ -0,0 +1,143 @@
+# Copyright The PyTorch Lightning team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from typing import Any, Callable, Optional
+
+import torch
+
+from pytorch_lightning.metrics.metric import Metric
+from pytorch_lightning.metrics.functional.r2score import (
+    _r2score_update,
+    _r2score_compute
+)
+
+
+class R2Score(Metric):
+    r"""
+    Computes r2 score also known as `coefficient of determination
+    <https://en.wikipedia.org/wiki/Coefficient_of_determination>`_:
+
+    .. math:: R^2 = 1 - \frac{SS_res}{SS_tot}
+
+    where :math:`SS_res=\sum_i (y_i - f(x_i))^2` is the sum of residual squares, and
+    :math:`SS_tot=\sum_i (y_i - \bar{y})^2` is total sum of squares. Can also calculate
+    adjusted r2 score given by
+
+    .. math:: R^2_adj = 1 - \frac{(1-R^2)(n-1)}{n-k-1}
+
+    where the parameter :math:`k` (the number of independent regressors) should
+    be provided as the `adjusted` argument.
+
+    Forward accepts
+
+    - ``preds`` (float tensor): ``(N,)`` or ``(N, M)`` (multioutput)
+    - ``target`` (float tensor): ``(N,)`` or ``(N, M)`` (multioutput)
+
+    In the case of multioutput, as default the variances will be uniformly
+    averaged over the additional dimensions. Please see argument `multioutput`
+    for changing this behavior.
+
+    Args:
+        num_outputs:
+            Number of outputs in multioutput setting (default is 1)
+        adjusted:
+            number of independent regressors for calculating adjusted r2 score.
+            Default 0 (standard r2 score).
+        multioutput:
+            Defines aggregation in the case of multiple output scores. Can be one
+            of the following strings (default is ``'uniform_average'``.):
+
+            * ``'raw_values'`` returns full set of scores
+            * ``'uniform_average'`` scores are uniformly averaged
+            * ``'variance_weighted'`` scores are weighted by their individual variances
+
+        compute_on_step:
+            Forward only calls ``update()`` and return None if this is set to False. default: True
+        dist_sync_on_step:
+            Synchronize metric state across processes at each ``forward()``
+            before returning the value at the step. default: False
+        process_group:
+            Specify the process group on which synchronization is called. default: None (which selects the entire world)
+
+    Example:
+
+        >>> from pytorch_lightning.metrics import R2Score
+        >>> target = torch.tensor([3, -0.5, 2, 7])
+        >>> preds = torch.tensor([2.5, 0.0, 2, 8])
+        >>> r2score = R2Score()
+        >>> r2score(preds, target)
+        tensor(0.9486)
+
+        >>> target = torch.tensor([[0.5, 1], [-1, 1], [7, -6]])
+        >>> preds = torch.tensor([[0, 2], [-1, 2], [8, -5]])
+        >>> r2score = R2Score(num_outputs=2, multioutput='raw_values')
+        >>> r2score(preds, target)
+        tensor([0.9654, 0.9082])
+    """
+    def __init__(
+        self,
+        num_outputs: int = 1,
+        adjusted: int = 0,
+        multioutput: str = "uniform_average",
+        compute_on_step: bool = True,
+        dist_sync_on_step: bool = False,
+        process_group: Optional[Any] = None,
+        dist_sync_fn: Callable = None,
+    ):
+        super().__init__(
+            compute_on_step=compute_on_step,
+            dist_sync_on_step=dist_sync_on_step,
+            process_group=process_group,
+            dist_sync_fn=dist_sync_fn,
+        )
+
+        self.num_outputs = num_outputs
+
+        if adjusted < 0 or not isinstance(adjusted, int):
+            raise ValueError('`adjusted` parameter should be an integer larger or'
+                             ' equal to 0.')
+        self.adjusted = adjusted
+
+        allowed_multioutput = ('raw_values', 'uniform_average', 'variance_weighted')
+        if multioutput not in allowed_multioutput:
+            raise ValueError(
+                f'Invalid input to argument `multioutput`. Choose one of the following: {allowed_multioutput}'
+            )
+        self.multioutput = multioutput
+
+        self.add_state("sum_squared_error", default=torch.zeros(self.num_outputs), dist_reduce_fx="sum")
+        self.add_state("sum_error", default=torch.zeros(self.num_outputs), dist_reduce_fx="sum")
+        self.add_state("residual", default=torch.zeros(self.num_outputs), dist_reduce_fx="sum")
+        self.add_state("total", default=torch.tensor(0), dist_reduce_fx="sum")
+
+    def update(self, preds: torch.Tensor, target: torch.Tensor):
+        """
+        Update state with predictions and targets.
+
+        Args:
+            preds: Predictions from model
+            target: Ground truth values
+        """
+        sum_squared_error, sum_error, residual, total = _r2score_update(preds, target)
+
+        self.sum_squared_error += sum_squared_error
+        self.sum_error += sum_error
+        self.residual += residual
+        self.total += total
+
+    def compute(self) -> torch.Tensor:
+        """
+        Computes r2 score over the metric states.
+        """
+        return _r2score_compute(self.sum_squared_error, self.sum_error, self.residual,
+                                self.total, self.adjusted, self.multioutput)
diff --git a/tests/metrics/regression/test_r2score.py b/tests/metrics/regression/test_r2score.py
new file mode 100644
index 0000000..ef3ec89
--- /dev/null
+++ b/tests/metrics/regression/test_r2score.py
@@ -0,0 +1,109 @@
+from collections import namedtuple
+from functools import partial
+
+import pytest
+import torch
+from sklearn.metrics import r2_score as sk_r2score
+
+from pytorch_lightning.metrics.regression import R2Score
+from pytorch_lightning.metrics.functional import r2score
+from tests.metrics.utils import BATCH_SIZE, NUM_BATCHES, MetricTester
+
+torch.manual_seed(42)
+
+num_targets = 5
+
+Input = namedtuple('Input', ["preds", "target"])
+
+_single_target_inputs = Input(preds=torch.rand(NUM_BATCHES, BATCH_SIZE), target=torch.rand(NUM_BATCHES, BATCH_SIZE),)
+
+_multi_target_inputs = Input(
+    preds=torch.rand(NUM_BATCHES, BATCH_SIZE, num_targets), target=torch.rand(NUM_BATCHES, BATCH_SIZE, num_targets),
+)
+
+
+def _single_target_sk_metric(preds, target, adjusted, multioutput):
+    sk_preds = preds.view(-1).numpy()
+    sk_target = target.view(-1).numpy()
+    r2_score = sk_r2score(sk_target, sk_preds, multioutput=multioutput)
+    if adjusted != 0:
+        r2_score = 1 - (1 - r2_score) * (sk_preds.shape[0] - 1) / (sk_preds.shape[0] - adjusted - 1)
+    return r2_score
+
+
+def _multi_target_sk_metric(preds, target, adjusted, multioutput):
+    sk_preds = preds.view(-1, num_targets).numpy()
+    sk_target = target.view(-1, num_targets).numpy()
+    r2_score = sk_r2score(sk_target, sk_preds, multioutput=multioutput)
+    if adjusted != 0:
+        r2_score = 1 - (1 - r2_score) * (sk_preds.shape[0] - 1) / (sk_preds.shape[0] - adjusted - 1)
+    return r2_score
+
+
+@pytest.mark.parametrize("adjusted", [0, 5, 10])
+@pytest.mark.parametrize("multioutput", ['raw_values', 'uniform_average', 'variance_weighted'])
+@pytest.mark.parametrize(
+    "preds, target, sk_metric, num_outputs",
+    [
+        (_single_target_inputs.preds, _single_target_inputs.target, _single_target_sk_metric, 1),
+        (_multi_target_inputs.preds, _multi_target_inputs.target, _multi_target_sk_metric, num_targets),
+    ],
+)
+class TestR2Score(MetricTester):
+    @pytest.mark.parametrize("ddp", [True, False])
+    @pytest.mark.parametrize("dist_sync_on_step", [True, False])
+    def test_r2(self, adjusted, multioutput, preds, target, sk_metric, num_outputs, ddp, dist_sync_on_step):
+        self.run_class_metric_test(
+            ddp,
+            preds,
+            target,
+            R2Score,
+            partial(sk_metric, adjusted=adjusted, multioutput=multioutput),
+            dist_sync_on_step,
+            metric_args=dict(adjusted=adjusted,
+                             multioutput=multioutput,
+                             num_outputs=num_outputs),
+        )
+
+    def test_r2_functional(self, adjusted, multioutput, preds, target, sk_metric, num_outputs):
+        self.run_functional_metric_test(
+            preds,
+            target,
+            r2score,
+            partial(sk_metric, adjusted=adjusted, multioutput=multioutput),
+            metric_args=dict(adjusted=adjusted,
+                             multioutput=multioutput),
+        )
+
+
+def test_error_on_different_shape(metric_class=R2Score):
+    metric = metric_class()
+    with pytest.raises(RuntimeError, match='Predictions and targets are expected to have the same shape'):
+        metric(torch.randn(100,), torch.randn(50,))
+
+
+def test_error_on_multidim_tensors(metric_class=R2Score):
+    metric = metric_class()
+    with pytest.raises(ValueError, match=r'Expected both prediction and target to be 1D or 2D tensors,'
+                                         r' but recevied tensors with dimension .'):
+        metric(torch.randn(10, 20, 5), torch.randn(10, 20, 5))
+
+
+def test_error_on_too_few_samples(metric_class=R2Score):
+    metric = metric_class()
+    with pytest.raises(ValueError, match='Needs atleast two samples to calculate r2 score.'):
+        metric(torch.randn(1,), torch.randn(1,))
+
+
+def test_warning_on_too_large_adjusted(metric_class=R2Score):
+    metric = metric_class(adjusted=10)
+
+    with pytest.warns(UserWarning,
+                      match="More independent regressions than datapoints in"
+                            " adjusted r2 score. Falls back to standard r2 score."):
+        metric(torch.randn(10,), torch.randn(10,))
+
+    with pytest.warns(UserWarning,
+                      match="Division by zero in adjusted r2 score. Falls back to"
+                            " standard r2 score."):
+        metric(torch.randn(11,), torch.randn(11,))