Despite several studies, the association of glucose intolerance with chronic hepatitis B (CHB) or C (CHC) virus infection remains controversial. We evaluated the prevalence of glucose intolerance by oral glucose tolerance test (OGTT) in patients with CHB or CHC in comparison with matched controls. In total, 189 consecutive outpatients with CHB or CHC and 189 subjects individually matched for age, sex and body mass index (BMI) were included. OGTT was performed in all cases, except in known diabetics, and glucose intolerance was defined as impaired glucose tolerance (IGT), OGTT-diabetes or known diabetes. Most patients with abnormal OGTT had normal fasting glucose (IGT: 69.8%, OGTT-diabetes: 54.5%). Compared with their own controls, CHB patients had a higher prevalence of IGT (13.6% vs 2.5%, P = 0.018) and family history of diabetes (34.6% vs 16.0%, P = 0.011), while CHC patents had higher prevalence of glucose intolerance (37.0% vs 15.7%, Rho = 0.001), mostly because of more frequent IGT (21.3% vs 6.5%, Rho = 0.003). After age and BMI adjustment, patients with CHC compared with those with CHB had significantly higher prevalence of glucose intolerance (37.0% vs 29.6%, P = 0.037). In conclusion, increased prevalence of glucose intolerance is documented by OGTT both in CHC and CHB patients compared with age, sex and BMI matched controls. Glucose intolerance is more frequent in CHC than CHB patients, regardless of known risk factors. An OGTT might be necessary at the baseline work-up of CHB or CHC patients, as a normal fasting glucose value does not exclude IGT or OGTT-diabetes.