Participants in a New York City WIC program were surveyed using a bilingual, self-administered questionnaire to determine significant differences in selected demographic, sociocultural, and educational characteristics of women who chose to breast feed versus bottle feed their infants. Differences in those characteristics were also compared for women breast feeding their infants for various lengths of time. Of the hypotheses tested, those with significant results included an increased incidence of breast feeding in women who had a higher educational attainment, entered prenatal care in the first trimester, had spent most of their lives outside the U.S., had the baby's father's support for breast feeding, and had previously breast fed. Increased duration of breast feeding was significantly associated with father's support of breast feeding, receipt of breast-feeding information, and the delayed introduction and infrequent use of breast-milk substitutes. The incidence of breast feeding reported (56.3%) compares favorably with rates reported for higher-income population segments. Early cessation of breast feeding was frequent; possible strategies to resolve this problem are presented.