The most recent Confidential Enquiry into the causes of maternal deaths during the perinatal period in England and Wales (1994–1996) revealed that psychological illness was at least as important as hypertensive disorders. It is therefore important for obstetricians to be aware of a variety of psychiatric conditions as well as the psychotropic medication prescribed and sequelae of continuation or withdrawal of these drugs. Best management, of this particularly vulnerable group of women, requires close liaison with the psychiatric team. This chapter considers four groups of women most likely to be prescribed psychoactive drugs during the perinatal period: (i) women with mental illness wishing to conceive, (ii) women with mental illness who conceive while taking medication, (iii) those who become mentally ill while pregnant, and (iv) those who become unwell postnatally. Guidelines for treatment are discussed.