BACKGROUND: Oral health status of individuals aged 3-80 years in the city of Jönköping, Sweden, has been assessed in a series of epidemiological studies over a 30-year period. AIM: To analyse the changes in caries prevalence and caries distribution in child population sample groups, based on studies performed in 1973, 1978, 1983, 1993, and 2003. DESIGN: Each time point included 500 randomly sampled individuals, divided into age groups of 3, 5, 10, 15, and 20 years. Results. Thirty-five per cent of 3-year-olds were caries free in 1973, compared with 69% 30 years later. Decayed and filled primary (dfs) and permanent surfaces (DFS) were reduced by 50-80% between 1973 and 2003. Adolescents aged 10 and 15 years exhibited the most pronounced reduction in DFS on the occlusal surfaces. By 2003, 90% of the proximal carious lesions in 15-year-olds were initial carious lesions. In 2003, about 60% of 15-year-olds had a DFS of < or = 5, while about 7% exhibited a DFS of > or = 26. CONCLUSIONS: Despite the dramatic decline in the prevalence of caries, caries remains a health problem among children, particularly those of preschool age. Continuous epidemiological studies are recommended to evaluate preventive measures.