Abstract Several investigators have reported high levels of gamma-glutamyl-transpeptidase (GGT) in the diabetic population. Therefore, we undertook a study to see the prevalence of ‘isolated’ high GGT in a large population of diabetics without chronic liver disease (CLD), as compared to an age- and sex-matched control group of non-diabetic subjects without CLD, and the role of extrahepatic factors in ‘isolated’ high GGT, as possible etiopathogenetic causes. We selected 351 diabetics with normal hepatologic screening, without echographic abnormalities of the hepatic parenchyma or the biliary tract. Age, duration and therapy of diabetes, body mass index (BMI), alcohol consumption, glycosylated hemoglobin (HbA1), and the presence of hepatitis B virus (HBV) were studied to see if they are related to high GGT. The control group included 260 age- and sex-matched non-diabetic subjects. We did not find any significant difference between diabetics and the control group in the prevalence of high GGT (men: 17.5% vs. 23%; women: 16% vs. 14.5%). Multiple regression analysis showed that alcohol consumption plays the major role in the high GGT of both men and women.