diff --git a/src/deepforest/main.py b/src/deepforest/main.py
index 45de757e..1101d7f6 100644
--- a/src/deepforest/main.py
+++ b/src/deepforest/main.py
@@ -853,8 +853,23 @@ def on_validation_epoch_end(self):
         self.log_epoch_metrics()
 
         if (self.current_epoch + 1) % self.config.validation.val_accuracy_interval == 0:
-            if len(self.predictions) > 0:
-                predictions = pd.concat(self.predictions)
+            # In DDP, each rank only has its share of validation batches in
+            # self.predictions. Gather from all ranks so metrics use the full set.
+            if self.trainer.world_size > 1 and torch.distributed.is_initialized():
+                object_list = [None] * self.trainer.world_size
+                torch.distributed.all_gather_object(object_list, self.predictions)
+                all_predictions = [
+                    df
+                    for rank_list in object_list
+                    for df in (rank_list if rank_list is not None else [])
+                ]
+                predictions = (
+                    pd.concat(all_predictions, ignore_index=True)
+                    if all_predictions
+                    else pd.DataFrame()
+                )
+            elif len(self.predictions) > 0:
+                predictions = pd.concat(self.predictions, ignore_index=True)
             else:
                 predictions = pd.DataFrame()