This article describes the aims, methods and baseline results of a project evaluating preventive measures within a selected high-risk group. In 1995 a cohort of 3373 12-year-olds was examined with regard to caries. A high-risk group was identified and randomly divided in four different groups, receiving different preventive programs. The whole study group will be examined every other year until the adolescents are 18 years old. The high-risk group will be examined every year and given the four different preventive measures until the adolescents are 18 years of age. A questionnaire will be answered by the adolescents every other year, in order to learn more about the links between demographic data, social background, lifestyle and health behaviour. Analysis of baseline results showed that the social distribution of the study group is comparable to that of the background population as well as to the distribution in rural and urban areas. The mean DMFT was 1.5, which is in accordance with the national figure. The 28 dentists who collect the data and perform the caries diagnostics were calibrated and the mean inter- and intra-reproducibility was 0.78 and 0.82, respectively. In conclusion, it seems that the study group is representative of 12-year-olds in Sweden; thus, inferences drawn from the results of the project may be valid for adolescents in Sweden as a whole.