Bipolar I (BPI) mood disorder is a severe recurrent mental Illness with a population prevalence of 1 percent. Evidence is strong for genetic risk factors in onset. However, unlike unipolar mood disorders, in which women outnumber men by 2 to 1, for BPI disorder, the male:female ratio is equal. Perhaps for this reason, relatively little research has examined gender-related risks in BPI course. This article presents data from 186 BPI women and 141 BPI men ascertained as part of the NIMH Genetics Initiative, a multisite collaborative molecular genetic study. Subjects were interviewed using the Diagnostic Interview for Genetic Studies (DIGS). DIGS items included a medical history, and for women, questions concerning psychiatric disorders in relation to childbearing, the menstrual cycle, and menopause. Almost half of BPI women who had been pregnant reported having experienced severe emotional disturbances in relation to childbearing, with close to one-third reporting episode onset during pregnancy. Two-thirds of BPI women reported frequent premenstrual mood disturbances and almost 20 percent of postmenopausal BPI women reported severe emotional disturbances during the menopausal transition. More BPI women than men reported thyroid disorder and migraine headaches. Findings are discussed in relation to gender differences in population and other clinical samples, and in terms of their implications for the development of new treatments and preventive interventions.