The aim of this study was to assess differences in oral health and dental behaviour in a cohort of five-year-old children born in 1982 and a cohort of eleven-year-old children born in 1976, in different ethnic and socio-economic groups, in the period from 1987 to 1990. To this end a secondary analysis was performed on data collected in a study monitoring the oral health of sick fund insured youths in The Netherlands. Large differences in dental health and dental health behaviour were found between ethnic and socio-economic strata. Thus, in the 1982 cohort, the caries prevalence and incidence were highest in the stratum of children of Turkish or Moroccan mothers with a low or unknown education. In the 1976 cohort, the caries prevalence and incidence were highest in children of Dutch parents with a low or unknown education. It is concluded that both stratification variables were caries risk indicators.