None of the 29 women with past episodes of postpartum psychosis experienced recurrences during pregnancy, even though they were not prophylactically treated with medication. In contrast, the 41 women with bipolar disorder experienced double the rate of recurrence when untreated (four of 10, or 40.0%) as when treated (six of 31, or 19.4%). Conversely, about 80% of the treated women and 60% of the untreated women with bipolar disorder remained well during pregnancy. After childbirth, all women with a history of postpartum psychosis (100.0%) remained well if they elected drug prophylaxis at delivery (20 of 29) and 55.6% (five of nine) of the women who declined prophylaxis were episode free. Among the 31 bipolar women who remained stable during pregnancy, 24 of 26 (92.3%) of those who used prophylaxis upon delivery remained well, and four of the remaining five women (80.0%) who declined prophylaxis remained well.