The risk for sudden infant death syndrome in black infants is twice that of white infants, and their parents are less likely to place them in the supine position for sleep. We previously identified barriers for parents to follow recommendations for sleep position. Our objective with this study was to quantify these barriers, particularly among low-income, primarily black mothers. We conducted face-to-face interviews with 671 mothers, 64% of whom were black, who attended Women, Infants, and Children Program centers in Boston, Massachusetts, Dallas, Texas, Los Angeles, California, and New Haven, Connecticut. We used univariate analyses to quantify factors that were associated with choice of sleeping position and multivariate logistic regression to calculate adjusted odds ratios for the 2 outcome variables: "ever" (meaning usually, sometimes, or last night) put infant in the prone position for sleep and "usually" put infant in the supine position to sleep. Fifty-nine percent of mothers reported supine, 25% side, 15% prone, and 1% other as the usual position. Thirty-four percent reported that they ever placed infants in the prone position. Seventy-two percent said that a nurse, 53% a doctor, and 38% a female friend or relative provided source of advice. Only 42% reported that a nurse, only 36% a doctor, and only 15% a female friend or relative recommended the supine position for sleep. When a female friend or relative recommended the prone position, mothers were more likely ever to place their infants in the prone position and less likely usually to choose supine compared with those who received no advice from friends or relatives. When a doctor or a nurse recommended a nonsupine position, the mothers were less likely to choose supine compared with those who received no advice from a doctor or a nurse. Mothers who trusted the opinion of a doctor or a nurse about infant sleeping position were more likely to place their infants in the supine position. Half of the mothers believed that infants were more likely to choke when supine, and they were less likely to place their infants supine. Mothers who believed that infants are more comfortable in the prone position (36%) were more likely to place their infants prone. Twenty-nine percent believed that having their infants sleep with an adult helps prevent sudden infant death syndrome, and only 43% believed that sudden infant death syndrome is related to sleeping position. We identified specific barriers to placing infants in the supine position for sleep (lack of or wrong advice, lack of trust in providers, knowledge and concerns about safety and comfort) in low-income, primarily black mothers that should be considered when designing interventions to get more infants onto their back for sleep.