Sleep problems are common in pregnant women. This review examines sleep in normal pregnancy; discusses the physiologic bases for alterations in sleep, including hormonal and mechanical factors; and correlates these factors with changes in sleep of pregnant women, as determined subjectively by surveys and objectively by polysomnographic studies. The changes in respiratory physiology during pregnancy, the possible predisposition of the pregnant woman to sleep-disordered breathing because of these changes, and results of published studies of sleep-disordered breathing in pregnancy are discussed. Finally, the effect of pregnancy on other sleep disorders and the management of these sleep disorders during pregnancy are outlined, including changes in management necessitated by this state. The paucity of available data and the need for further studies of incidence and outcomes of sleep disorders in the pregnant woman are emphasized.