OBJECTIVE This study estimated the prevalence of early childhood caries (ECC) and related behavioral risk factors in a population of low-income, Mexican-American children in Stockton, California. METHODS We collected data for 220 children ages six years or less using a parent-completed questionnaire and clinical dental examinations during the Su Salud Health and Education Fair in July 1995. We employed five case definitions of ECC: buccal or lingual caries on one or two primary maxillary incisors; caries on any surface of one or two primary maxillary incisors; and five decayed, missing (due to caries), or filled primary teeth. RESULTS The prevalence of ECC ranged from 12.3 percent to 30.5 percent, depending upon the case definition. More than 17 percent of children age two years had one primary maxillary incisor affected by caries on the buccal or lingual surface; 13.2 percent had two affected. Mean age at weaning from breast--or bottle-feeding and patterns of bottle use during sleep did not differ significantly between children with ECC and those without. There were no clear patterns of cariogenic food frequency and disease status. CONCLUSIONS Our findings question whether feeding patterns with human breast milk, formula, or bovine milk are sufficient etiologic factors for this condition.