Objective: to systematically compare methods and some findings from two prospective cohort studies of oral health. Methods: This paper describes and compares two such population-based birth cohort studies of younger adults: the Dunedin Multidisciplinary Health and Development Study (conducted in New Zealand); and the 1982 Pelotas Birth Cohort Study (conducted in Brazil). Results: The two cohorts showed sociodemographic similarities and differences, with their gender mixes being similar, but their ethnic compositions differing markedly. There were some important similarities and differences in methods. Overall dental caries experience was higher among the Dunedin cohort. Each of the studies has examined the association between childhood-adulthood changes in socio-economic status and oral health in the mid-20s. Both studies observed the greatest disease experience among those who were of low SES in both childhood and adulthood, and the least among those who were of high SES in both childhood and adulthood. In each cohort, disease experience in the upwardly mobile and downwardly mobile groups lay between those two extremes. Conclusions and implications: There are important similarities and differences in both methods and findings. While the need for a degree of methodological convergence in future is noted, the two studies are able to use each other as replicate samples for research into chronic oral conditions. © 2011 The Authors.