[Individual and contextual determinants of the prevalence of untreated caries in Brazil]. 
To describe the prevalence of untreated caries among adolescents in Brazil and to analyze the association between caries and individual and contextual factors in the municipalities where these adolescents live.  A Ministry of Health database (projeto SB-Brasil) provided health records on 16 833 adolescents from 15-19 years of age.  The study variable used was the presence of at least one permanent tooth having been lost to caries.  The individual variables considered were: sex, ethnic group, living in an urban versus a rural area, and being a student or not.  Contextual variables related to the municipality were: municipal human development index (MHDI), proportion of households connected to the water system, and water fluoridation for 5 years or more.  Multilevel logistic regression analysis was carried out to adjust the outcome to the individual and contextual variables.  Individual determinants related to a higher probability of untreated caries were: the ethnic group described as "black or brown," (adjusted odds ratio, OR(adjust) = 1.79; 1.68 to 1.92); and living in a rural area (OR(adjust) = 1.31; 1.19 to 1.45).  Being a student was identified as a protective factor (OR(adjust) = 0.67; 0.62 to 0.73).  Secondary variables identified as contextual determinants of caries were MHDI (adjusted coefficient beta = -0.213), water fluoridation (beta = -0.201), and households connected to the water system (beta = -0.197).  The results show inequalities in the distribution of health services in the various Brazilian regions, and suggest that inequalities may also be present in the effectiveness of the services provided.  Policies to increase access to fluoride-treated water and school enrollment may contribute to preventing caries in adolescents.