diff --git a/cg/services/order_validation_service/models/errors.py b/cg/services/order_validation_service/models/errors.py
index 2bbec19056..e6297f9fa3 100644
--- a/cg/services/order_validation_service/models/errors.py
+++ b/cg/services/order_validation_service/models/errors.py
@@ -53,3 +53,8 @@ class OrderNameRequiredError(OrderError):
 class OccupiedWellError(CaseSampleError):
     field: str = "well_position"
     message: str = "Well is already occupied"
+
+
+class ReusedSampleNameError(CaseSampleError):
+    field: str = "name"
+    message: str = "Sample name already used"
diff --git a/cg/services/order_validation_service/workflows/tomte/validation/inter_field/rules.py b/cg/services/order_validation_service/workflows/tomte/validation/inter_field/rules.py
index 8142989ed6..1f136f9414 100644
--- a/cg/services/order_validation_service/workflows/tomte/validation/inter_field/rules.py
+++ b/cg/services/order_validation_service/workflows/tomte/validation/inter_field/rules.py
@@ -1,9 +1,13 @@
-from cg.services.order_validation_service.models.errors import OccupiedWellError
+from cg.services.order_validation_service.models.errors import (
+    OccupiedWellError,
+    ReusedSampleNameError,
+)
 from cg.services.order_validation_service.workflows.tomte.models.order import TomteOrder
 from cg.services.order_validation_service.workflows.tomte.validation.inter_field.utils import (
     _get_errors,
     _get_excess_samples,
     _get_plate_samples,
+    get_duplicate_sample_name_errors,
 )
 
 
@@ -11,3 +15,11 @@ def validate_wells_contain_at_most_one_sample(order: TomteOrder) -> list[Occupie
     samples_with_cases = _get_plate_samples(order)
     samples = _get_excess_samples(samples_with_cases)
     return _get_errors(samples)
+
+
+def validate_unique_sample_names_in_cases(order: TomteOrder) -> list[ReusedSampleNameError]:
+    errors: list[ReusedSampleNameError] = []
+    for case in order.cases:
+        case_errors = get_duplicate_sample_name_errors(case)
+        errors.extend(case_errors)
+    return errors
diff --git a/cg/services/order_validation_service/workflows/tomte/validation/inter_field/utils.py b/cg/services/order_validation_service/workflows/tomte/validation/inter_field/utils.py
index c056dc4ba3..501a20ebd3 100644
--- a/cg/services/order_validation_service/workflows/tomte/validation/inter_field/utils.py
+++ b/cg/services/order_validation_service/workflows/tomte/validation/inter_field/utils.py
@@ -1,5 +1,9 @@
+from collections import Counter
 from cg.models.orders.sample_base import ContainerEnum
-from cg.services.order_validation_service.models.errors import OccupiedWellError
+from cg.services.order_validation_service.models.errors import (
+    OccupiedWellError,
+    ReusedSampleNameError,
+)
 from cg.services.order_validation_service.workflows.tomte.models.case import TomteCase
 from cg.services.order_validation_service.workflows.tomte.models.order import TomteOrder
 from cg.services.order_validation_service.workflows.tomte.models.sample import (
@@ -47,3 +51,14 @@ def _get_sample_well_map(plate_samples_with_cases: list[tuple[TomteSample, Tomte
             sample_well_map[sample.well_position] = []
         sample_well_map[sample.well_position].append((sample, case))
     return sample_well_map
+
+
+def get_duplicate_sample_names(case: TomteCase) -> list[str]:
+    sample_names = [sample.name for sample in case.samples]
+    count = Counter(sample_names)
+    return list({name for name, freq in count.items() if freq > 1})
+
+
+def get_duplicate_sample_name_errors(case: TomteCase) -> list[ReusedSampleNameError]:
+    sample_names = get_duplicate_sample_names(case)
+    return [ReusedSampleNameError(sample_name=name, case_name=case.name) for name in sample_names]