Most of the caries of African child populations is found in limited fractions of that population. The purpose of the present study was to analyze the caries situation of Sierra Leonean schoolchildren in relation to demographic, socioeconomic, and behavioral variables, in order to develop an appropriate index for prediction of caries. A total of 610 students from primary class 1 (mean age: 7 yr) and secondary form 1 (mean age 15 yr) were dentally examined by three examiners and interviewed by their teachers. Intra- and interexaminer reproducibilities were 82 and 70%, and interinterviewer reliability was 67-100% for the individual questions. Urban students had more caries than rural. In class 1, dmfs+DMFS was 4.1 and 1.8, respectively; in form 1, DMFS was 5.3 and 3.5. Two tribes (the Fulas and the Madingos) had higher caries means than the rest, especially in class 1, where dmfs+DMFS was 6.5 and 2.4, respectively. Form 1 students with literate parents had a higher caries mean, and class 1 pupils with defective school uniforms a lower mean. The apparently high-risk groups did not consume more sweet snacks or clean their teeth less frequently. There was clearly more caries among the quartiles of children with most visible plaque on molars, but all social and demographic subgroups had similar amounts of plaque. Multivariate analyses of class 1 children showed that pupils living in urban areas, Fulas and Madingos, and children wearing complete school uniforms had caries significantly more frequently, other factors being equal.(ABSTRACT TRUNCATED AT 250 WORDS)