OBJECTIVE To determine, for different age groups, the approximal caries increment in a three-year longitudinal retrospective study and to investigate the relationship between the caries increment and self-reported measures for oral health behaviour, dental knowledge and attitude (cynicism, health concern and motivation). METHODS 14, 17, 20 and 23-year-olds, who participated in a clinical epidemiological survey. Bitewings were taken of approximately 52% of the participants. Longitudinally, three cohorts were followed radiographically for three years. The self-reported measures were derived from questionnaires with sufficient reliability. RESULTS For all participants, on average, 3.7 enamel lesions and 1.2 dentine lesions were found. The number of sound surfaces, adequate restorations and the D1FS score showed significant differences over a three-year period, for all age groups. Stepwise regression analysis showed that for the explanation of the change in number of sound surfaces, number of enamel lesions and D1S between the age of 17 and 20, the variable 'health concern' contributed significantly to the regression. The change in D3FS score was explained by the variable 'behaviour', while the change in D1Fs score was explained by both 'behaviour' and 'health concern'. Neither of the dental variables, 'dental knowledge' or 'motivation' contributed significantly. For the ages 14-17 and 20-23 no significant contributions were found. CONCLUSIONS A considerable caries increment was found in this three-year retrospective radiographic study, which was not related to dental knowledge and motivation, and only for one age group (17-20) to oral health behaviour and health concern.