OBJECTIVE There are few studies of caries development and caries-related factors from early age to young adulthood. The aim of the present study is to analyse caries prevalence in 20-year-olds in relation to their previous caries experience. METHODS Oral health from 3 to 20 years of age was followed longitudinally in a cohort of 499 individuals. The clinical and radiographic incidence of caries and restorations in 494 20-year-olds was related to caries data at 3, 6 and 15 years of age. RESULTS Twenty-six per cent of the 20-year-olds were caries-free. The mean number of initial and manifest lesions and restorations (Di + mFS) was 5.8. Initial lesions comprised 40% of the Di + mFS. Of the occlusal surfaces of molars and premolars, 12 and 4%, respectively, had manifest caries or restorations. Compared with individuals who had been caries-free during childhood (primary dentition) and adolescence, those with a history of caries activity while growing up had statistically significantly more approximal lesions at the age of 20 (DmFSa 0.6 vs. DmFSa 4.6, respectively). Those with manifest caries during childhood but caries-free at 15 years had a low caries prevalence at 20 years of age (DmFSa 1.3). Few new lesions developed after age 15. However, 50% of initial lesions at this age had progressed to manifest lesions at age 20. CONCLUSIONS There is a relationship between caries prevalence at age 20 and early caries experience.