Seven women with histories of puerperal psychosis and four with histories of puerperal major depression were consecutively treated with high-dose oral estrogen immediately following delivery. None of the women had histories of nonpuerperal affective disorder, and all women were affectively well throughout the current pregnancy and at delivery. Despite the high risk for recurrent illness in this population, only one woman developed relapse of postpartum affective disorder. All others remained entirely well and required no treatment with psychotropic medications during the 1 year follow-up period. This low rate of relapse, 9% compared to an expected 35-60% without prophylaxis, suggests that oral estrogen may stem the rapid rate of change in estrogen following delivery, thereby preventing the potential impact on dopaminergic and serotonergic neuroreceptors. It is hypothesized that the rapid rate of change of estrogen after delivery creates an "estrogen withdrawal state." This may be a critical factor in driving acute puerperal affective psychosis and early-onset puerperal major depression.