The weeks following childbirth are a period of high risk in bipolar women with manic or mixed affective episodes following 20-30% of deliveries. Although the vast majority of episodes have their onset within 2 weeks of delivery it is commonly believed that there is a "latent" or symptom-free period in the first few days after delivery. We examine the day of onset of clinically significant symptoms in 101 bipolar women who have experienced an episode of puerperal (postpartum) psychosis. We find no evidence of a latent period. Over 50% of symptom onsets occur on days 1-3, with over 22% occurring on the first postpartum day.