Despite the importance of early initiation of and exclusive breastfeeding, prelacteal feeds continue to pose a barrier to optimal breastfeeding practices in several countries. This study examined the factors associated with prelacteal feeding among Vietnamese mothers in 2011. During the first three days after birth, 73.3% of the newborns were fed prelacteals, most commonly infants formula and water. The odds of feeding prelacteals declined with increased breastfeeding knowledge, beliefs about social norms in favor of exclusive breastfeeding, and confidence in one’s own breastfeeding behaviors. Women who harbored misconceptions about breastfeeding had twice the odds of feeding any prelacteals. Health care factors and difficulties also increased the odds of prelacteal feeding. Health staff support during pregnancy and after birth reduced the odds of feeding formula. The multiple factors contributing to the high prevalence of prelacteal feeding behaviors stress the need for early and appropriate breastfeeding interventions in Viet Nam, particularly during routine healthcare contacts.