The aim of the present study was to evaluate the prevalence of caries and caries associated variables in 15-year-olds in relation to foreign background and to examine differences in the prevalence of caries in immigrant adolescents according to their length of residence in Sweden. All 15-year-old adolescents (n=143) at one public school in the city of Jönköping, Sweden were asked to participate in the study. The adolescents were divided into two groups according to their background: immigrants and non-immigrants. Data on caries prevalence were extracted from the dental records of the examination made when the participants were 15 years old. The proportions of immigrants and non-immigrants free from carious lesions were equal. Immigrant adolescents, however, had on average more enamel carious lesions. Adolescents born in Sweden of immigrant parents or who had arrived before 1 year of age had a caries prevalence similar to those of non-immigrant adolescents, whereas children who had immigrated to Sweden after 7 years of age had a caries prevalence that was 2-3 times higher. As the caries carious lesions in immigrant adolescents is mainly restricted to the enamel, and possibly reversible, early introduction of preventive programmes seems essential.