Prepregnant overweight and obesity have been associated with failure to initiate and to sustain breastfeeding (BF) among Caucasian women; however, this relationship has not been studied among either Black or Hispanic women. Information extracted from medical records was used to examine the relationship between prepregnant overweight (BMI = 26.1-29.0 kg/m(2)) and obesity (BMI > 29.0 kg/m(2)) and the initiation and duration of BF among Black and Hispanic women living in an urban area. Among 587 Hispanic women, those who were obese were more likely than normal-weight women to feed formula and breast milk rather than to feed breast milk alone before discharge [odds ratio (OR): 1.9; 95% CI: 1.2-3.1]. Obese Hispanic women also had higher rates of discontinuation of exclusive BF [relative risk (RR): 1.5; 95% CI: 1.1-2.0]) and higher rates of discontinuation of BF to any extent (RR: 1.5; 95% CI: 1.1-2.1) during the first 6 mo postpartum. Among 640 Black women, prepregnant BMI was neither associated with differences in feeding pattern before discharge nor with differences in rates of discontinuation of exclusive or any BF. We concluded that among healthy women who attempt to breastfeed in the hospital, maternal prepregnant obesity was negatively associated with initiation and duration of BF in Hispanic women. In contrast, prepregnant BMI did not have the same association among Black women who attempted to breastfeed. We speculate that obesity may have a different biological meaning for BF success in Black women than it does in those who are Caucasian or Hispanic.