diff --git a/.gitignore b/.gitignore
index 4124b2bf1..df22aa7de 100644
--- a/.gitignore
+++ b/.gitignore
@@ -29,3 +29,8 @@ dist/
 /datasets
 /models
 /output
+
+/inference
+last_checkpoint
+log.txt
+
diff --git a/configs/e2e_mask_rcnn_R_50_FPN_1x.yaml b/configs/e2e_mask_rcnn_R_50_FPN_1x.yaml
index 7f5a8941c..305cab30c 100644
--- a/configs/e2e_mask_rcnn_R_50_FPN_1x.yaml
+++ b/configs/e2e_mask_rcnn_R_50_FPN_1x.yaml
@@ -30,7 +30,8 @@ MODEL:
     SHARE_BOX_FEATURE_EXTRACTOR: False
   MASK_ON: True
 DATASETS:
-  TRAIN: ("coco_2014_train", "coco_2014_valminusminival")
+  TRAIN: ("coco_2014_train",)
+  VAL: ("coco_2014_valminusminival",)
   TEST: ("coco_2014_minival",)
 DATALOADER:
   SIZE_DIVISIBILITY: 32
diff --git a/maskrcnn_benchmark/config/defaults.py b/maskrcnn_benchmark/config/defaults.py
index ddc2c4e21..11edc0470 100644
--- a/maskrcnn_benchmark/config/defaults.py
+++ b/maskrcnn_benchmark/config/defaults.py
@@ -67,6 +67,8 @@
 _C.DATASETS = CN()
 # List of the dataset names for training, as present in paths_catalog.py
 _C.DATASETS.TRAIN = ()
+# List of the dataset names for validating, as present in paths_catalog.py
+_C.DATASETS.VAL = ()
 # List of the dataset names for testing, as present in paths_catalog.py
 _C.DATASETS.TEST = ()
 
diff --git a/maskrcnn_benchmark/data/build.py b/maskrcnn_benchmark/data/build.py
index d2895fd7e..eada5227a 100644
--- a/maskrcnn_benchmark/data/build.py
+++ b/maskrcnn_benchmark/data/build.py
@@ -9,12 +9,13 @@
 
 from . import datasets as D
 from . import samplers
+from .dataset_mode import DatasetMode
 
 from .collate_batch import BatchCollator
 from .transforms import build_transforms
 
 
-def build_dataset(dataset_list, transforms, dataset_catalog, is_train=True):
+def build_dataset(dataset_list, transforms, dataset_catalog, mode=DatasetMode.TRAIN):
     """
     Arguments:
         dataset_list (list[str]): Contains the names of the datasets, i.e.,
@@ -22,7 +23,7 @@ def build_dataset(dataset_list, transforms, dataset_catalog, is_train=True):
         transforms (callable): transforms to apply to each (image, target) sample
         dataset_catalog (DatasetCatalog): contains the information on how to
             construct a dataset.
-        is_train (bool): whether to setup the dataset for training or testing
+        mode (DatasetMode): whether to setup the dataset for training, validation, or testing
     """
     if not isinstance(dataset_list, (list, tuple)):
         raise RuntimeError(
@@ -36,16 +37,16 @@ def build_dataset(dataset_list, transforms, dataset_catalog, is_train=True):
         # for COCODataset, we want to remove images without annotations
         # during training
         if data["factory"] == "COCODataset":
-            args["remove_images_without_annotations"] = is_train
+            args["remove_images_without_annotations"] = mode != DatasetMode.TEST
         if data["factory"] == "PascalVOCDataset":
-            args["use_difficult"] = not is_train
+            args["use_difficult"] = mode == DatasetMode.TEST
         args["transforms"] = transforms
         # make dataset from factory
         dataset = factory(**args)
         datasets.append(dataset)
 
     # for testing, return a list of datasets
-    if not is_train:
+    if mode != DatasetMode.TEST:
         return datasets
 
     # for training, concatenate all datasets into a single one
@@ -104,9 +105,9 @@ def make_batch_data_sampler(
     return batch_sampler
 
 
-def make_data_loader(cfg, is_train=True, is_distributed=False, start_iter=0):
+def make_data_loader(cfg, mode=DatasetMode.TRAIN, is_distributed=False, start_iter=0):
     num_gpus = get_world_size()
-    if is_train:
+    if mode == DatasetMode.TRAIN:
         images_per_batch = cfg.SOLVER.IMS_PER_BATCH
         assert (
             images_per_batch % num_gpus == 0
@@ -115,6 +116,7 @@ def make_data_loader(cfg, is_train=True, is_distributed=False, start_iter=0):
         images_per_gpu = images_per_batch // num_gpus
         shuffle = True
         num_iters = cfg.SOLVER.MAX_ITER
+        dataset_list = cfg.DATASETS.TRAIN
     else:
         images_per_batch = cfg.TEST.IMS_PER_BATCH
         assert (
@@ -125,6 +127,7 @@ def make_data_loader(cfg, is_train=True, is_distributed=False, start_iter=0):
         shuffle = False if not is_distributed else True
         num_iters = None
         start_iter = 0
+        dataset_list = cfg.DATASETS.TEST if mode == DatasetMode.TEST else cfg.DATASETS.VAL
 
     if images_per_gpu > 1:
         logger = logging.getLogger(__name__)
@@ -148,10 +151,9 @@ def make_data_loader(cfg, is_train=True, is_distributed=False, start_iter=0):
         "maskrcnn_benchmark.config.paths_catalog", cfg.PATHS_CATALOG, True
     )
     DatasetCatalog = paths_catalog.DatasetCatalog
-    dataset_list = cfg.DATASETS.TRAIN if is_train else cfg.DATASETS.TEST
 
-    transforms = build_transforms(cfg, is_train)
-    datasets = build_dataset(dataset_list, transforms, DatasetCatalog, is_train)
+    transforms = build_transforms(cfg, mode)
+    datasets = build_dataset(dataset_list, transforms, DatasetCatalog, mode)
 
     data_loaders = []
     for dataset in datasets:
@@ -168,8 +170,8 @@ def make_data_loader(cfg, is_train=True, is_distributed=False, start_iter=0):
             collate_fn=collator,
         )
         data_loaders.append(data_loader)
-    if is_train:
-        # during training, a single (possibly concatenated) data_loader is returned
+    if mode != DatasetMode.TEST:
+        # during training and validation, a single (possibly concatenated) data_loader is returned
         assert len(data_loaders) == 1
         return data_loaders[0]
     return data_loaders
diff --git a/maskrcnn_benchmark/data/dataset_mode.py b/maskrcnn_benchmark/data/dataset_mode.py
new file mode 100644
index 000000000..ff1eec86d
--- /dev/null
+++ b/maskrcnn_benchmark/data/dataset_mode.py
@@ -0,0 +1,8 @@
+# Author: Petr Vytovtov <p.vytovtov@partner.samsung.com>
+from enum import Enum
+
+
+class DatasetMode(Enum):
+    TRAIN = 1
+    VALID = 2
+    TEST = 3
diff --git a/maskrcnn_benchmark/data/transforms/build.py b/maskrcnn_benchmark/data/transforms/build.py
index 88aa975b6..8468d4b27 100644
--- a/maskrcnn_benchmark/data/transforms/build.py
+++ b/maskrcnn_benchmark/data/transforms/build.py
@@ -1,9 +1,10 @@
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 from . import transforms as T
+from maskrcnn_benchmark.data.dataset_mode import DatasetMode
 
 
-def build_transforms(cfg, is_train=True):
-    if is_train:
+def build_transforms(cfg, mode=DatasetMode.TRAIN):
+    if mode == DatasetMode.TRAIN:
         min_size = cfg.INPUT.MIN_SIZE_TRAIN
         max_size = cfg.INPUT.MAX_SIZE_TRAIN
         flip_prob = 0.5  # cfg.INPUT.FLIP_PROB_TRAIN
diff --git a/maskrcnn_benchmark/engine/trainer.py b/maskrcnn_benchmark/engine/trainer.py
index 281d91339..ddfe20f99 100644
--- a/maskrcnn_benchmark/engine/trainer.py
+++ b/maskrcnn_benchmark/engine/trainer.py
@@ -6,7 +6,7 @@
 import torch
 import torch.distributed as dist
 
-from maskrcnn_benchmark.utils.comm import get_world_size
+from maskrcnn_benchmark.utils.comm import get_world_size, synchronize
 from maskrcnn_benchmark.utils.metric_logger import MetricLogger
 
 from apex import amp
@@ -45,6 +45,7 @@ def do_train(
     device,
     checkpoint_period,
     arguments,
+    data_loader_val=None,
 ):
     logger = logging.getLogger("maskrcnn_benchmark.trainer")
     logger.info("Start training")
@@ -107,6 +108,37 @@ def do_train(
             )
         if iteration % checkpoint_period == 0:
             checkpointer.save("model_{:07d}".format(iteration), **arguments)
+            if data_loader_val is not None:
+                meters_val = MetricLogger(delimiter="  ")
+                synchronize()
+                with torch.no_grad():
+                    for idx_val, (images_val, targets_val, _) in enumerate(data_loader_val):
+                        images_val = images_val.to(device)
+                        targets_val = [target.to(device) for target in targets_val]
+                        loss_dict = model(images_val, targets_val)
+                        losses = sum(loss for loss in loss_dict.values())
+                        loss_dict_reduced = reduce_loss_dict(loss_dict)
+                        losses_reduced = sum(loss for loss in loss_dict_reduced.values())
+                        meters_val.update(loss=losses_reduced, **loss_dict_reduced)
+                synchronize()
+                logger.info(
+                    meters_val.delimiter.join(
+                        [
+                            "[Validation]: ",
+                            "eta: {eta}",
+                            "iter: {iter}",
+                            "{meters}",
+                            "lr: {lr:.6f}",
+                            "max mem: {memory:.0f}",
+                        ]
+                    ).format(
+                        eta=eta_string,
+                        iter=iteration,
+                        meters=str(meters_val),
+                        lr=optimizer.param_groups[0]["lr"],
+                        memory=torch.cuda.max_memory_allocated() / 1024.0 / 1024.0,
+                    )
+                )
         if iteration == max_iter:
             checkpointer.save("model_final", **arguments)
 
diff --git a/tools/test_net.py b/tools/test_net.py
index c666a4655..73a1bc21e 100644
--- a/tools/test_net.py
+++ b/tools/test_net.py
@@ -9,6 +9,7 @@
 import torch
 from maskrcnn_benchmark.config import cfg
 from maskrcnn_benchmark.data import make_data_loader
+from maskrcnn_benchmark.data.dataset_mode import DatasetMode
 from maskrcnn_benchmark.engine.inference import inference
 from maskrcnn_benchmark.modeling.detector import build_detection_model
 from maskrcnn_benchmark.utils.checkpoint import DetectronCheckpointer
@@ -87,7 +88,7 @@ def main():
             output_folder = os.path.join(cfg.OUTPUT_DIR, "inference", dataset_name)
             mkdir(output_folder)
             output_folders[idx] = output_folder
-    data_loaders_val = make_data_loader(cfg, is_train=False, is_distributed=distributed)
+    data_loaders_val = make_data_loader(cfg, mode=DatasetMode.TEST, is_distributed=distributed)
     for output_folder, dataset_name, data_loader_val in zip(output_folders, dataset_names, data_loaders_val):
         inference(
             model,
diff --git a/tools/train_net.py b/tools/train_net.py
index 9f4761b3f..bd5d8fd0d 100644
--- a/tools/train_net.py
+++ b/tools/train_net.py
@@ -13,6 +13,7 @@
 import torch
 from maskrcnn_benchmark.config import cfg
 from maskrcnn_benchmark.data import make_data_loader
+from maskrcnn_benchmark.data.dataset_mode import DatasetMode
 from maskrcnn_benchmark.solver import make_lr_scheduler
 from maskrcnn_benchmark.solver import make_optimizer
 from maskrcnn_benchmark.engine.inference import inference
@@ -67,10 +68,15 @@ def train(cfg, local_rank, distributed):
 
     data_loader = make_data_loader(
         cfg,
-        is_train=True,
+        mode=DatasetMode.TRAIN,
         is_distributed=distributed,
         start_iter=arguments["iteration"],
     )
+    data_loader_val = make_data_loader(
+        cfg,
+        mode=DatasetMode.VALID,
+        is_distributed=distributed,
+    )
 
     checkpoint_period = cfg.SOLVER.CHECKPOINT_PERIOD
 
@@ -83,6 +89,7 @@ def train(cfg, local_rank, distributed):
         device,
         checkpoint_period,
         arguments,
+        data_loader_val,
     )
 
     return model
@@ -104,7 +111,7 @@ def run_test(cfg, model, distributed):
             output_folder = os.path.join(cfg.OUTPUT_DIR, "inference", dataset_name)
             mkdir(output_folder)
             output_folders[idx] = output_folder
-    data_loaders_val = make_data_loader(cfg, is_train=False, is_distributed=distributed)
+    data_loaders_val = make_data_loader(cfg, mode=DatasetMode.TEST, is_distributed=distributed)
     for output_folder, dataset_name, data_loader_val in zip(output_folders, dataset_names, data_loaders_val):
         inference(
             model,