diff --git a/scripts/importer/validateData.py b/scripts/importer/validateData.py
index 913f7069..e945a596 100644
--- a/scripts/importer/validateData.py
+++ b/scripts/importer/validateData.py
@@ -91,6 +91,11 @@
 # global character limit on sample stable ids
 MAX_SAMPLE_STABLE_ID_LENGTH = 63
 
+# global character limit on clinical attribute values; matches the
+# `clinical_patient`/`clinical_sample` ATTR_VALUE varchar(255) database columns,
+# beyond which values would be silently truncated on load
+MAX_CLINICAL_ATTRIBUTE_VALUE_LENGTH = 255
+
 # global variable that defines the invalid ID characters
 INVALID_ID_CHARACTERS = r"[^A-Za-z0-9._()\[\]',+\-:;]"
 
@@ -2750,6 +2755,18 @@ def checkLine(self, data):
                 value = data[col_index].strip()
             data_type = self.attr_defs[col_index]['datatype']
 
+            # values are stored in a varchar(255) column and would be silently
+            # truncated on load if they are longer than that
+            if len(value) > MAX_CLINICAL_ATTRIBUTE_VALUE_LENGTH:
+                self.logger.error(
+                    'Value exceeds the maximum length of %d characters and '
+                    'would be truncated when loaded' %
+                    MAX_CLINICAL_ATTRIBUTE_VALUE_LENGTH,
+                    extra={'line_number': self.line_number,
+                           'column_number': col_index + 1,
+                           'column_name': col_name,
+                           'cause': value[:50] + '...'})
+
             # if not blank, check if values match the datatype
             if value.strip().lower() in self.NULL_VALUES:
                 pass
diff --git a/tests/test_data/data_clin_value_too_long.txt b/tests/test_data/data_clin_value_too_long.txt
new file mode 100644
index 00000000..307aa86b
--- /dev/null
+++ b/tests/test_data/data_clin_value_too_long.txt
@@ -0,0 +1,7 @@
+#Patient Identifier	Sample Identifier	Subtype
+#Identifier to uniquely specify a patient.	A unique sample identifier.	Subtype description.
+#STRING	STRING	STRING
+#1	1	1
+PATIENT_ID	SAMPLE_ID	SUBTYPE
+TEST-PAT1	TEST-PAT1-SAMPLE1	AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+TEST-PAT2	TEST-PAT2-SAMPLE1	BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
diff --git a/tests/unit_tests_validate_data.py b/tests/unit_tests_validate_data.py
index 2ae21efc..947c131b 100755
--- a/tests/unit_tests_validate_data.py
+++ b/tests/unit_tests_validate_data.py
@@ -368,6 +368,25 @@ def test_sample_with_invalid_characters_in_sample_id(self):
         self.assertEqual(record.line_number, 11)
         self.assertIn('PATIENT_ID and SAMPLE_ID can only contain letters, numbers, points, underscores and/or hyphens', record.getMessage())
 
+    def test_clinical_attribute_value_too_long(self):
+        """Test that a value exceeding the maximum length raises an error.
+
+        Clinical attribute values are stored in a varchar(255) column, so a
+        longer value would be silently truncated on load. The boundary value of
+        exactly 255 characters is accepted, while 256 characters is rejected.
+        """
+        self.logger.setLevel(logging.ERROR)
+        record_list = self.validate('data_clin_value_too_long.txt',
+                                    validateData.SampleClinicalValidator)
+        # only the 256-character value (line 7) should be flagged; the
+        # 255-character value on line 6 is allowed
+        self.assertEqual(1, len(record_list))
+        record = record_list.pop()
+        self.assertEqual(logging.ERROR, record.levelno)
+        self.assertEqual(7, record.line_number)
+        self.assertEqual(3, record.column_number)
+        self.assertIn('maximum length', record.getMessage())
+
 
 
 class PatientAttrFileTestCase(PostClinicalDataFileTestCase):