OBJECTIVES: To describe the occurrence and severity of dental caries in children and adolescents and to relate these findings to the subject's socio-cultural and socio-economic backgrounds. MATERIAL AND METHODS: A cross-sectional study in 12 706 children aged 5, 7, 12 and 15 years was conducted in 2006. Data on children's caries experience were collected from public oral health registers and pooled with socio-cultural and socio-economic data obtained from official statistics. The study population represented 76% of all registered inhabitants. RESULTS: Among 5- and 7-year-old children with non-Danish mothers, the mean caries experience was three to four times higher than among children of Danish mothers, and a doubled rate was seen among the adolescents (p < 0.001). Significant differences in caries experience were found in various ethnic minorities. Multiple regression analysis showed that the level of caries was highest among children in families where mothers were not Danish, with low income, where mothers' educational levels were low, and in with a high number of children (p < 0.001). CONCLUSIONS: Although almost all children and adolescents attend the prevention-oriented, free public dental service, a social gradient still exists for dental health. In addition, in all age groups, major inequalities in dental health were found when families with Danish and non-Danish backgrounds were compared. The findings indicate a need for social action by policymakers. Furthermore, a change in the oral health preventive strategy is proposed to meet the needs of children in risk of caries, and appropriate oral health-promotion programmes should be organized in collaboration with leaders from different ethnic minorities.