An epidemiologic study was carried out between April 1981 and March 1982 to determine the total caries experience of 8-yr-old Nigerian children in both the private and the government schools in Lagos. A total of 860 children were examined for the study. 451 were from free, non-fee paying government schools while 409 were from the fee-paying private schools. 50.1% were boys and 49.9% were girls. The mean dmf score for private schoolchildren is 1.5 and that of the government schoolchildren is 1.1. This difference is statistically significant (P less than 0.001). The mean dmf score for the whole sample is 1.3. The mean DMF for the private schoolchildren is 0.55 while that of the government schoolchildren is 0.24. This difference is statistically significant (P less than 0.001). The mean DMF for all the children examined is 0.4. The mean dmf score for boys (1.3) is slightly higher than the mean dmf score for girls (1.2), while the mean DMF score for girls (0.5) is higher than that for boys (0.4). These sex differences are thought to be due to slight differences in the eruption times. There is no difference between the sexes in the proportion of children who are caries-free (52.9% boys and 52% girls). Some 46% of the private schoolchildren were caries-free compared with 58.3% of those in the government schools. This difference is statistically significant (P less than 0.001). This difference is thought to be due to the greater consumption of refined carbohydrates by the private schoolchildren, who come from the higher socioeconomic strata of the community.(ABSTRACT TRUNCATED AT 250 WORDS)