Background: Previous studies have demonstrated that breastfed newborns spend more time awake than bottle‐fed newborns, breastfeeding mothers have more fragmented sleep than bottle‐feeding mothers, and mother‐newborn sleeping arrangements may affect the sleep/wake pattern of mother‐newborn pairs. Objective: To address the unsolved question of whether there is an interaction between type of feeding and sleeping arrangements that affects postpartum sleep during the 4th postpartum week. Design: Correlational, two‐way design using feeding method and location of newborn at night as independent variables, and sleep patterns as the dependent variables.Setting: Patient's home during 4th week after giving birth. Patients/Participants: First‐time mothers and their newborns (n = 33). Main Outcome Measures: Amount of total sleep, amount of night sleep, number of night awakenings, and number of sleep periods in 24 hours using a modified version of the self‐report sleep instrument by Barnard and Eyres. Results: Breastfed newborns had less total sleep per day than bottle‐fed newborns, and breastfeeding mothers had more sleep periods in 24 hours than bottle‐feeding mothers. Breastfeeding mothers slept more than bottle‐feeding mothers when co‐sleeping, but bottle‐feeding mothers’ sleep was unaffected by location of newborn. Average total sleep for 4‐week‐old newborns was about 14 hours daily. Conclusions: More sleep was obtained when breastfeeding mothers slept with the newborn. Methods or devices that allow breastfeeding mothers and newborns to sleep next to each other in complete safety need to be developed.