OBJECTIVE: To describe the distribution of caries in 12-year-old children in Sweden according to socio-demographic and oral health related behaviour. PARTICIPANTS: The study group consisted of 3,373 12-year-old children residing in catchments of 26 different public dental health clinics in Sweden, geographically well represented. METHOD: The clinical examination for dental caries was performed by 28 calibrated dentists. A questionnaire on lifestyle was distributed to the children with questions on ethnicity, socio-economic level and oral health as well as overall health attitudes. RESULTS: The proportion of 12-year-old children with no experience of dentine caries was 47% and 35% were completely free from all caries. Intraoral distribution of caries showed most lesions on the first molar mesial surface, with 80% enamel and 20% dentine caries. Almost all children brushed their teeth twice a day and a third of the children had an extra intake of fluoride. Decayed surfaces including enamel caries (DeS) was chosen as a measure of ongoing caries and used when dividing children into three caries groups; caries free (50%), 1-3 lesions (40%) and the high caries group (10%) with more than 3 lesions. These groups showed distribution differences. More non-Swedish children, children from workers' homes, and children who brushed their teeth less than twice a day were found in the high caries group. More children from workers' homes living in big cities and snacking more than once a week were also found in the high caries group. This could not be shown for other social groups. Also children who had an extra intake of fluoride were classified in the high caries group.