BACKGROUND: The use of an oral glucose tolerance test (OGTT) has been recommended to diagnose type 2 diabetes, but an OGTT with venous blood sampling may not be feasible in the screening phase preceding large epidemiological studies. We have conducted a population-based screening in 2715 men and women and evaluated the diagnostic validity of capillary plasma glucose concentration measurements versus venous plasma glucose concentration measurements in a subset of 350 subjects. METHODS: During a single OGTT, glucose concentrations were measured in venous plasma as well as in capillary plasma. RESULTS: Based on the 1999 WHO criteria for venous glucose concentrations, the study population (n=350) yielded 97 subjects with type 2 diabetes mellitus, 77 subjects with impaired glucose tolerance and 176 subjects with normal glucose tolerance. Sensitivity and specificity to diagnose type 2 diabetes mellitus by capillary plasma were 84% and 98%, respectively. Consistent classification by either venous or capillary plasma glucose measurements was 78% (kappa=0.65, p<0.001). CONCLUSION: Capillary glucose measurements are suitable for use in epidemiological studies to diagnose and detect type 2 diabetes and normal glucose tolerance. Use of capillary measurements can result in cost-effective inclusion schemes in epidemiological studies.