BACKGROUND AND OBJECTIVES: The American Academy of Pediatrics recommends infants be placed supine for sleep. Our objectives in this study were to, in a nationally representative sample, examine (1) prevalence of maternal intention regarding infant sleeping position and of actual practice and (2) factors associated with their choices. METHODS: We recruited mothers from 32 US hospitals, oversampling African American and Hispanic mothers, in a nationally representative sample of mothers of infants aged 2 to 6 months. Survey questions assessed choice of usual infant sleeping position, all sleeping positions, intention for sleep position, as well as actual practice. Multivariable logistic regression analyses controlled for demographic, receipt of doctor advice, and theory of planned behavior variables (attitudes, subjective norms, and perceived control). RESULTS: Of the 3297 mothers, 77.3% reported they usually placed their infants in the supine position for sleep, but fewer than half reported that they exclusively did so. Only 43.7% of mothers reported that they both intended to and then actually placed their infants exclusively supine. African American mothers and those who did not complete high school were more likely to intend to use the prone position. Theory of planned behavior factors (attitudes, subjective norms, and perceived control) and doctor advice were associated with maternal choice. CONCLUSIONS: Not all mothers place their infants exclusively supine for sleep. Many mothers intend to place their infants supine yet often do not do so in actual practice. Factors potentially amenable to intervention including attitudes, subjective norms, and doctor advice are associated with intention and practice.