The influence of sociodemographic factors on the incidence and duration of breast-feeding was evaluated in 668 black and 511 white women delivering their first child in the metropolitan Washington, DC, area. Breast-feeding rates were 84% among white and 49% among black women. Maternal educational level was strongly associated with breast-feeding, whereas the effect of ethnicity was moderate. Women with some college or some graduate school education had adjusted odds of breast-feeding that were 2.6 (95% confidence limit 1.9 to 3.7) and 5.2 (95% confidence limit 2.7 to 10.2) times higher than women with a high school education or less. In contrast, the adjusted odds of breast-feeding were 2.0 (95% confidence limit 1.4 to 3.1) times higher for white women compared with black women. The odds of breast-feeding increased among black women if they attended childbirth classes, were married, or were older. Among black women, the frequency of breast-feeding decreased sharply by 1 month postpartum. Breast-feeding duration for black v white women was 74% v 90% at 1 month, 44% v 72% at 4 months, and 26% v 50% at 7 months postpartum. The majority of black women (53%) used formula supplements in the hospital, which was the only factor significantly related to a shortened duration in this group (P less than .01). The high rate of formula supplementation among black women and its strong association with shortened duration of breast-feeding point to a need for more advice and support and less reliance on formula during the hospital stay.