The aim of this study was to analyze the occurrence of EFD lesions in relation to some background factors in Finnish and Soviet children. Children aged 7, 9 and 12 years (n = 1187) were examined clinically in Helsinki, Kuopio (Finland), Moscow and Leningrad (USSR). A questionnaire sent to the parents was used to collect data on toothbrushing frequency, use of sweets, cakes, soft drinks, sugar-sweetened tea/coffee and mother's education. In addition to bivariate analysis, log-linear regression models were used for comparing the simultaneous association in two ethnic groups. In general, the Finnish children had more EFD lesions than the Soviet children did. Among the Finns no consistent associations were found between the number of EFD lesions and the use of different sugar products or differences in toothbrushing habits. The number of EFD lesions decreased consistently according to mother's education with the Finnish children, but not with the Soviet children. The final multivariate model for Finnish children included age, toothbrushing frequency, place of residence (Kuopio) and use of soft drinks. The respective model for the Soviet children included age and place of residence (Leningrad). Evidently, the demineralization process or tooth resistance differs in these two ethnic groups.