Glucose intolerance is associated with chronic liver disease, particularly cirrhosis, and overt diabetes mellitus is two to four times more common than in the general population. Little attention has been paid to the relationship between the cause of cirrhosis and the development of glucose intolerance or whether cirrhosis is a prerequisite. We found glucose intolerance to be particularly common in patients with chronic hepatitis C, and in this retrospective study we attempt to confirm this possible association. To investigate this question we reviewed the files of 128 patients with chronic hepatitis C and 40 with chronic hepatitis B and active liver disease. Demographic, laboratory, imaging and pathology data were ed. The mean fasting blood glucose (+/-SD) in the hepatitis C and B groups was 160 +/- 83 and 103 +/- 18 mg/dl (P < 0.0001) with 2.5% and 39.1% respectively being overtly diabetic (P < 0.00001). However, the mean age of the hepatitis C group was much higher (45.6 +/- 12.5 vs. 60.1 +/- 12.3 years, P < 0.00001). The prevalence of diabetes was much higher among the hepatitis C patients than in the general population. Cirrhosis was not more frequent in biopsies from hepatitis C diabetic patients compared with non-diabetic or hepatitis B patients. Multivariate analysis showed that type of hepatitis and age were significant and independent predictors for developing diabetes. We conclude that there appears to be an association between diabetes mellitus and chronic hepatitis C that is not present in patients with chronic hepatitis B.