Sleep disruption has been suggested to contribute to postpartum mood, but few studies have explored differences in this relationship between nulliparous and multiparous mothers. This study compared the interaction of sleep and mood as a function of parity. Thirty-five nulliparous and 34 multiparous mothers completed questionnaires on mood and sleep, and wore actigraphs for 7 days during the third trimester of pregnancy and within 2 weeks postpartum. Mood and objective sleep were better in multiparas than in nulliparas after delivery. However, other than a stronger association between subjective sleep and stress in nulliparous mothers, the relationship between sleep and mood did not differ significantly between the two groups. This suggests that parity might play only a limited role in the interaction between sleep and mood during the immediate postpartum period.