To identify and characterize health care system factors that contribute to successful breastfeeding in the early postpartum period. A prospective 8-week cohort study of 522 women at five area hospitals who had a vaginal delivery of a healthy, full-term single child and who intended to breastfeed. Mothers and infants had free access to each other for breastfeeding during the hospital stay. Data were obtained through chart review and surveys. In-person postpartum interviews in the hospital and 4- and 8-week telephone interviews were used to determine participants' perceptions of breastfeeding support by hospital personnel, home visit nurses, and family and friends. The hospital in-person interview with each mother was conducted before discharge to confirm maternal interest and intent to breastfeed. Questions were asked regarding breastfeeding information and support provided by medical and nursing personnel. Mothers were asked to rate the quality of information, as well as the degree of support they received for breastfeeding. Mothers also were asked to rate their hospital breastfeeding experience. A second interview was conducted by telephone 4 weeks after birth. The focus of this interview was to ascertain the rating of their breastfeeding experience, the quality of their interactions with health care professionals, and whether supplemental formula was being provided to the infant. If supplemental formula was being provided, the mothers were asked to quantify the volume and frequency of supplementation. A final telephone interview was conducted when the infants were 8 weeks of age. This interview determined the continuance or cessation of breastfeeding and information about formula supplementation, as in the 4-week interview. Mothers were given a journal and asked to note all telephone calls, clinic visits, and home nurse visits that related to breastfeeding issues and concerns. Demographic data examined included maternal age, marital status, highest level of education reached, race, employment, insurance coverage, and length of stay in the hospital. Pregnancy characteristics included prenatal care, parity, and gravity. Infant characteristics included gestational age and birth weight. Other factors examined included maternal rating of the support received from the infant's father for the decision to breastfeed, the time the infant spent in the mother's hospital room, and whether the infant was breastfed in the delivery room. The women were mostly white (90%), educated (82% had some college education), married, older (mean maternal age of 29.3 years), and insured (92% commercial). The primary outcome of interest was success at breastfeeding. Success was determined based on each mother's initial estimate of the planned duration of breastfeeding. Of the participants, 76% breastfed successfully for at least as long as they had initially planned. Seventeen percent of the mothers had stopped breastfeeding at the time of the 4-week interview, and 29% had stopped by the 8-week interview. Of the infants' fathers, 97% were reported by the mothers to be supportive of the decision to breastfeed. Once discharged, 98% of mothers expected to have help with the household chores. Eighty percent rated their hospital breastfeeding experience as good or very good. However, only 56% rated hospital breastfeeding support as good or very good, and only 44% spoke with a lactation consultant while in the hospital. Of those who spoke with the lactation consultant, 85% felt more confident afterward. Hospital nurses talked with 82% of women, and 97% of these found this helpful. Seventy-four percent reported receiving a home nursing visit after discharge, and of these, 82% found it helpful. Successful mothers were significantly more likely to report that the visiting nurse watched them breastfeed and asked how it was going. Mothers were more likely to call or visit family and friends with concerns about breastfeeding than