OBJECTIVE To screen adolescents at risk of type 2 diabetes mellitus (T2DM) using random capillary blood glucose (RCBG). METHODS Ninth grade pupils who were overweight and/or had a family history of T2DM were offered to have RCBG measured and were referred for further investigation if the value was > or = 7.8 mmol/L. RESULTS Two thousand four hundred and eleven pupils were examined, 19% were overweight, 4% being obese. 589 met inclusion criteria and 384 participated. Ethnic minorities and pupils in low socio-economic school-areas (SESA) were significantly more overweight than ethnic Danes and pupils in high SESA. Compared to ethnic Danish pupils, the relative risk of having a positive parent history of T2DM was increased five-fold for ethnic Turkish and Arab pupils and 13-fold for ethnic Pakistani pupils. One pupil had a diagnosed T2DM. Two had elevated RCBG values. One of these had an undiagnosed T2DM. CONCLUSIONS Our study shows a high prevalence of overweight adolescents in Copenhagen, especially in school areas with low socio-economic standard and in pupils with Turkish, Pakistani and Arab ethnicity. Only three out of the 10 pupils with the highest risk participated. New strategies to reach and motivate risk groups to follow health recommendations and new methods of screening should be developed.