Aims: To describe the variation in the estimated prevalence of diabetes and impaired glucose regulation (IGR) within Europe in relation to age and body mass index (BMI). Methods: Cross-sectional data from European population-based studies with both fasting and 2-h glucose after a standard 75-g oral glucose tolerance test were included (9449 men, 7752 women). Results: There was a large variation in the estimated prevalence of diabetes and impaired glucose regulation among 11 European centres, ranging from 2% to 24% for diabetes and 5% to 43% for IGR. In cross-sectional analysis the estimated prevalence of diabetes and IGR increased with age and BMI. The impact of age did not differ between centres with similar age range, and the impact of BMI was similar in most centres. Conclusions: Differences in age and BMI within Europe partly explained the variation in estimates of the IGR and diabetes prevalence. The impact of age and BMI did not differ between centres. Variations in prevalence must therefore be due to other factors that we could not adjust for, such as methodology, differences in diet, physical activity and genetic predisposition.