Electroencephalographic (EEG) sleep was examined longitudinally in 34 obstetrically healthy volunteers recruited early in pregnancy. All women were free of current psychiatric disorder. Fourteen women had a personal history of affective disorder, and 20 had no history of any psychiatric disorder. EEG sleep was recorded in subjects' homes at specified points from 12 weeks' gestation through 8 months' postpartum to examine the impact of childbearing on sleep and psychiatric symptoms in women with a history of affective disorder. EEG sleep measurements, as well as clinical ratings of sleep, indicated that sleep disturbances were most pronounced over the first 2 to 3 months' postpartum and were characterized primarily by interrupted sleep. The obstetrical course of these women was uneventful, and the outcome with respect to affective disturbances was highly favorable. Nevertheless, childbearing was associated with greater changes in total sleep time and with rapid eye movement (REM) latency reduction in women with a history of affective disorder, even in the absence of clinically significant mood changes. Findings suggest that the sleep system of women with a history of affective disorder may be more sensitive to the psychobiological changes associated with childbearing, as evidenced by earlier onset of sleep disruption over the childbearing course and a reduction in REM latency in the final trimester that persisted throughout the eighth postpartum month.