It is commonly believed that the prevalence of dental caries in developing countries is increasing, though in Kenya and Tanzania there is insufficient information to confirm such trends. In order to test the hypothesis, therefore, 762 children in Dar es Salaam and 802 children in Nairobi aged 12 yr in 1984 were examined for dental caries as part of a baseline study to monitor changes of prevalence with time. Dental caries was recorded by surfaces using the criteria recommended by the WHO and examinations were performed by standardized examiners. The mean DMFT in Dar es Salaam of 0.67 (SD 1.20) was significantly higher than that for Nairobi, 0.51 (SD 1.23). No differences were found in the mean DMFS index. Nairobi children had a greater number of filled teeth and surfaces. Although a greater proportion of children were caries-free in Nairobi than in Dar es Salaam, amongst those with caries, Nairobi children had significantly higher DMFS scores, and a greater proportion with DMFS greater than 4. The possible reasons for such findings are discussed. The mean DMFT and DMFS reported here are amongst the lowest reported in the recent literature from both countries.