To examine the impact of postpartum sleep disturbance on 24-hour milk volume and breastfeeding during the early postpartum period. Factors associated with postpartum sleep disturbance also were examined. A descriptive, correlational design was used. The sample included 29 first-time mothers exclusively breastfeeding healthy, full-term newborns. A home visit was conducted to collect self-report data for sleep, stress, fatigue, depression, and anxiety at 2 weeks postpartum. Infant test weights as an estimate of 24-hour milk volume also were performed. At 1 month, a phone interview was conducted for breastfeeding status. Pearson's correlation and hierarchical regression were used for data analysis. All mothers were breastfeeding at 2 weeks and at 1 month postpartum. Most (69.2%) reported significant sleep disturbance. Higher degree of stress was associated with more disturbed sleep (β = .59, p = .001), and sleep disturbance was associated with more symptoms of fatigue (r = .70, p = - .001), depression (r = .58, p = .001), and anxiety (r = .52, p = - .01). Poor sleep quality was the only significant predictor for lower milk volume (β = - .70, p = .02). Clinically significant sleep disturbance is common during the early postpartum period and may have a negative impact on human milk production and other important maternal health indicators. A better understanding of postpartum sleep disturbance and its impact on breastfeeding and maternal health is needed.