AIM: To prospectively investigate serum CA 19-9 levels in type 2 diabetic patients in comparison with age- and gender-matched control subjects. METHODS: We recorded duration of diabetes and examined fasting glucose levels, HbA1c levels and serum CA 19-9 levels in 76 type 2 diabetic patients and 76 controls. Abdominal CT was performed in order to eliminate abdominal malignancy in the diabetic and control groups. RESULTS: The average CA 19-9 level was 46.0 ± 22.4 U/mL for diabetic patients whereas it was 9.97 ± 7.1 U/mL for the control group (P ＜ 0.001 ). Regression analysis showed a positive correlation between diabetes and CA 19-9 independent from age, gender, glucose level and HbA1c level (t = 8.8, P ＜ 001 ). Two of the diabetic patients were excluded from the study because of abdominal malignancy shown by CT at the initial evaluation. For all patients, abdominal CT showed no pancreatic abnormalities. CONCLUSION: CA 19-9 is a tumor-associated antigen, which is elevated in pancreatic, upper gastrointestinal tract, ovarian hepatocellular, and colorectal cancers, as well as in inflammatory conditions of the hepatobiliary system, biliary obstruction and in thyroid diseases. Diabetes has been claimed to be a risk factor for pancreatic cancer, which is increasing its incidence and has one of the lowest survival rates of all cancers. CA 19-9 is used in the diagnosis of pancreatic cancer but is also a marker of pancreatic tissue damage that might be caused by diabetes. We propose that a higher cutoff value of CA 19-9 should be used in diabetics to differentiate benign and malignant pancreatic disease, and subtle elevations of CA 19-9 in diabetics should be considered as the indication of exocrine pancreatic dysfunction.