Women with a history of bipolar affective disorder or postpartum affective psychosis have a greatly increased risk for recurrence of psychosis following subsequent pregnancies. The use of lithium carbonate for prophylaxis of postpartum psychosis in such women remains controversial. Four women are described with a history of puerperal affective psychosis, who were given lithium prophylactically following delivery and had no recurrence of postpartum psychosis. The rationale for the timing, dosage, and monitoring of lithium administration in this situation is discussed. Given the apparent safety of lithium prophylaxis relative to the dangers of postpartum affective psychosis, more effort should be directed to definitive research to resolve whether lithium prophylaxis is indicated for this population, as contemporary knowledge and these four cases would suggest.