It is generally understood that the teeth of pre-school-aged children are healthy, but the improvement in the dmft index has halted in the industrialized countries. Those few children who have caries have more of it than before. Little is known of the family-related factors which are associated with this polarization of caries. A representative population-based sample consisted of 1443 mothers expecting their first child. The children were followed at well-baby clinics and public dental health clinics for over five years. The objective was to study the prevalence of dental caries and its predictors in five-year-old children and to assess children's own dental health habits and the meaning of family-related factors in dental health. The findings were based on questionnaire data from parents and on clinical dental examinations of the five-year-old children as completed by 101 public health dentists. In firstborn five-year-old children, dental health was found to be good in 72%, fair in 20%, and poor in 8% of the cases. The final multivariate analysis illustrated that the dmft index > 0 was independently associated with the mother's irregular toothbrushing (OR 2.2; 95% CI 1.4-3.5), annual occurrence of several carious teeth in the father (OR 2.6; 95% CI 1.9-3.6), daily sugar consumption at the age of 18 months (OR 2.4; 95% CI 1.4-4.1), occurrence of child's headaches (OR 3.7; 95% CI 1.5-8.8), parents' cohabitation (OR 3.3; 95% CI 1.5-7.6), rural domicile (OR 2.4; 95% CI 1.2-4.5), and mother's young age (OR 5.0; 95% CI 1.3-19.8). The findings indicated that attention should be paid not only to the child's dental health care but also to that of the whole family. Parents should be supported in their upbringing efforts and encouraged to improve their children's dental health habits. In everyday life, parents function as role models for their children, and therefore, parents' own dental hygiene habits are very meaningful.