This study was conducted to examine associations among breastfeeding duration, child care arrangement, and participation in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). The authors analyzed the nationally representative sample of infants born in 2001 who were enrolled in the Early Childhood Longitudinal Study-Birth Cohort (9 months). They estimated the risks of short breastfeeding duration (< 6 months of age) among infants according to the child care arrangement and WIC participation (n = 7515). Approximately 50% of US infants were enrolled in WIC, and 47% received child care on a regular basis. Both WIC participation and child care use were independently associated with short breastfeeding duration. Compared to those under parental care, WIC participants under relative care were more likely to discontinue breastfeeding before the age of 6 months. A breastfeeding support program targeted toward relative care users may be useful for WIC participants.