Background: Although much research has focused on identifying factors that influence breastfeeding initiation and duration, many high-risk factors are nonmodifiable demographic variables. Predisposing factors for low breastfeeding duration rates that are amenable to supportive interventions should be identified. The purpose of this study was to assess the effect of maternal confidence (breastfeeding self-efficacy) on breastfeeding duration. Method: A prospective survey was conducted with 300 women in the last trimester of pregnancy recruited from the antenatal clinic of a large metropolitan hospital in Brisbane, Australia. Telephone interviews were conducted at 1week and 4 months postpartum to assess infant feeding methods and breastfeeding confidence using the Breastfeeding Self-Efficacy Scale. Results: Although 92 percent of participants initiated breastfeeding, by 4 months postpartum almost 40 percent of mothers discontinued and only 28.6 percent were breastfeeding exclusively; the most common reason for discontinuation was insufficient milk supply. Antenatal and 1-week Breastfeeding Self-Efficacy Scale scores were significantly related to breastfeeding outcomes at 1 week and 4 months. Mothers with high breastfeeding self-efficacy were significantly more likely to be breastfeeding, and doing so exclusively, at 1 week and 4 months postpartum than mothers with low breastfeeding self-efficacy. Conclusions: Maternal breastfeeding self-efficacy is a significant predictor of breastfeeding duration and level. Integrating self-efficacy enhancing strategies may improve the quality of care that health care professionals deliver and may increase a new mother's confidence in her ability to breastfeed, and to persevere if she does encounter difficulties.