diff --git a/src/icosagon/loss.py b/src/icosagon/loss.py
new file mode 100644
index 0000000..eb2e0fe
--- /dev/null
+++ b/src/icosagon/loss.py
@@ -0,0 +1,44 @@
+import torch
+from icosagon.trainprep import PreparedData
+from icosagon.declayer import Predictions
+
+
+class CrossEntropyLoss(torch.nn.Module):
+    def __init__(self, data: PreparedData, partition_type: str = 'train',
+        reduction: str = 'sum', **kwargs) -> None:
+
+        super().__init__(**kwargs)
+
+        if not isinstance(data, PreparedData):
+            raise TypeError('data must be an instance of PreparedData')
+
+        if partition_type not in ['train', 'val', 'test']:
+            raise ValueError('partition_type must be set to train, val or test')
+
+        if reduction not in ['sum', 'mean']:
+            raise ValueError('reduction must be set to sum or mean')
+
+        self.data = data
+        self.partition_type = partition_type
+        self.reduction = reduction
+
+    def forward(self, pred: Predictions) -> torch.Tensor:
+        input = []
+        target = []
+        for fam in pred.relation_families:
+            for rel in fam.relation_types:
+                for edge_type in ['edges_pos', 'edges_back_pos']:
+                    x = getattr(getattr(rel, edge_type), self.partition_type)
+                    assert len(x.shape) == 1
+                    input.append(x)
+                    target.append(torch.ones_like(x))
+                for edge_type in ['edges_neg', 'edges_back_neg']:
+                    x = getattr(getattr(rel, edge_type), self.partition_type)
+                    assert len(x.shape) == 1
+                    input.append(x)
+                    target.append(torch.zeros_like(x))
+        input = torch.cat(input, dim=0)
+        target = torch.cat(target, dim=0)
+        res = torch.nn.functional.binary_cross_entropy(input, target,
+            reduction=self.reduction)
+        return res
diff --git a/tests/icosagon/test_loss.py b/tests/icosagon/test_loss.py
new file mode 100644
index 0000000..07e5e5c
--- /dev/null
+++ b/tests/icosagon/test_loss.py
@@ -0,0 +1,40 @@
+from icosagon.loss import CrossEntropyLoss
+from icosagon.declayer import Predictions, \
+    RelationFamilyPredictions, \
+    RelationPredictions
+from icosagon.data import Data
+from icosagon.trainprep import prepare_training, \
+    TrainValTest
+import torch
+
+
+def test_cross_entropy_loss_01():
+    d = Data()
+    d.add_node_type('Dummy', 5)
+    fam = d.add_relation_family('Dummy-Dummy', 0, 0, False)
+    fam.add_relation_type('Dummy Rel', torch.tensor([
+        [0, 1, 0, 0, 0],
+        [1, 0, 0, 0, 0],
+        [0, 0, 0, 1, 0],
+        [0, 0, 0, 0, 1],
+        [0, 1, 0, 0, 0]
+    ], dtype=torch.float32))
+
+    prep_d = prepare_training(d, TrainValTest(1., 0., 0.))
+
+    rel_pred = RelationPredictions(
+        TrainValTest(torch.tensor([1, 0, 1, 0, 1], dtype=torch.float32), torch.zeros(0), torch.zeros(0)),
+        TrainValTest(torch.zeros(0), torch.zeros(0), torch.zeros(0)),
+        TrainValTest(torch.zeros(0), torch.zeros(0), torch.zeros(0)),
+        TrainValTest(torch.zeros(0), torch.zeros(0), torch.zeros(0))
+    )
+    fam_pred = RelationFamilyPredictions([ rel_pred ])
+    pred = Predictions([ fam_pred ])
+
+    loss = CrossEntropyLoss(prep_d)
+    print('loss: %.7f' % loss(pred))
+    assert torch.abs(loss(pred) - 55.262043) < 0.000001
+
+    loss = CrossEntropyLoss(prep_d, reduction='mean')
+    print('loss: %.7f' % loss(pred))
+    assert torch.abs(loss(pred) - 11.0524082) < 0.000001