ObjectiveTo identify factors related to breastfeeding self-efficacy, an important psychological variable in sustained breastfeeding, in the postpartum period. DesignDescriptive correlational study. SettingData were collected on the mother–baby unit of an academic medical center in the Northeastern United States. ParticipantsThis convenience sample (N = 107) was composed of women in the first 4 days postpartum and included nearly equal numbers of primiparas (49.5%, n = 53) and multiparas (50.5%, n = 54). MethodsParticipants completed the Perceived Stress Scale–10, Birth Satisfaction Scale–Revised, Breastfeeding Self-Efficacy Scale–Short Form, and a demographic questionnaire. Descriptive and inferential statistics were used to analyze the data. ResultsBreastfeeding self-efficacy was positively correlated with birth satisfaction, number of children, partner support of breastfeeding, intention to breastfeed, intention to breastfeed exclusively for 6 months, and feeling prepared for birth. Breastfeeding self-efficacy was greater in women with previous breastfeeding experience and lower in mothers of newborns who received in-hospital formula supplementation. A standard multiple linear regression explained approximately 38.5% of the variance in self-efficacy scores. ConclusionNurses can apply our findings to inform strategies to increase breastfeeding confidence, such as promoting birth satisfaction, involving partners in breastfeeding education, and limiting the use of in-hospital formula supplementation.