Background: Although some women experience anger as a mood problem after childbirth, postpartum anger has been neglected by researchers. Poor maternal and infant sleep quality during the postpartum period has been associated with depressive symptoms; however, links between sleep quality and postpartum anger are unclear. This study aimed to determine the proportions of women with significant anger, depressive symptoms, and comorbid anger and depressive symptoms, and to examine maternal and infant sleep quality as correlates of postpartum anger. Methods: This cross-sectional survey study was advertised as an examination of mothers’ and babies’ sleep. Women, with healthy infants between 6 and 12 months of age, were recruited using social media. The survey contained validated measures of maternal and infant sleep quality, and maternal fatigue, social support, anger, depressive symptoms, and cognitions about infant sleep. Results: 278 women participated in the study. Thirty-one percent of women (n = 85) reported high anger levels (≥ 90th percentile on State Anger Scale) while 26% (n = 73) of mothers indicated probable depression (>12 on Edinburgh Postnatal Depression Scale). Women reported a mean of 6.2 hours of sleep (SD = 1.2 hours, range = 4 – 9 hours); over half of the participants rated their sleep as poor (n = 144, 51.8 %). Using robust regression analysis, income (b = -0.74, p < 0.05), parity (b = 2.05, p < 0.01), depressive symptoms (b = 0.59, p < 0.01), maternal sleep quality (b = 0.98, p < 0.05), and maternal anger about infant sleep (b = 0.50, p < 0.01) were significant predictors of maternal anger. Conclusions: Maternal sleep quality and anger about infant sleep are associated with maternal state anger. Clinicians should educate families about sleep pattern changes during the perinatal time frame and assess women’s mood and perceptions of maternal and infant sleep quality in the first postpartum year. They can also offer evidence-based strategies for improving parent-infant sleep. Such health promotion initiatives could reduce maternal anger and support healthy maternal-infant sleep.