This study sought to determine the prevalence of early childhood caries and the oral health habits of children ages 0 to 4 years in Macau, China vs. children in Hong Kong. Caregivers of 353 children from 7 nursery centers completed a questionnaire, and dental personnel examined their children with a light and disposable mouth mirror. The children's mean age was 2.8 +/- 0.6 years. Using the diagnostic criterion that cavitation was evidence of dental caries, the caries prevalence was 18%. When the age range was narrowed to 1.8 to 3.5 years, the caries prevalence was 19% in Macau children compared to 17% in Hong Kong children. No statistically significant relationship existed among caries prevalence, feeding habits, or oral hygiene habits, supporting the notion that the etiology of ECC is multifactorial. The similarity of caries prevalence in these 2 populations may result from the effects of cultural norms on the dental habits of the children.