There is increasing awareness of the influence of female reproductive life events on the course of bipolar disorder. Here, we describe the case histories of 5 women diagnosed with postpartum psychosis who subsequently experienced major mood disorders in relation to the perimenopause. This case series suggests that (a) the perimenopause may be a time of increased risk for women who experienced postpartum bipolar episodes and (b) periods of hormonal change represent a major trigger for bipolar episodes in some women.