PURPOSE: This study investigated the prevalence and etiological factors associated with caries in a group of young Australian aboriginal children from 1 to 3.5 years of age. METHODS: One hundred and forty-seven healthy infants, aged from 1 to 3.5 years, attending a community health center in Brisbane, a nonfluoridated state capital city, were randomly selected for the study. RESULTS: The caries prevalence was 39% by subjects and 32% by the total number of teeth present. The mean number of decayed, filled teeth (dtf) was 2.5 +/- 0.4, which is more than twice the figure for 3-year-old children in Australia. Furthermore, the filled (f) component represented only 1% of the total dft, suggesting very low treatment levels. Increased caries experience of the infants was strongly associated with high dental plaque scores, high levels of Streptococcus mutans infection, and sleep-time consumption of milk containing added sugar. CONCLUSION: The results suggest that urban Australian aboriginal infants are at high risk for caries, and that preventive strategies are urgently required.