We interviewed 128 women regularly during pregnancy and the first postnatal year. Psychiatric interviews identified eight 'cases' of psychiatric disorder (6 per cent) in early pregnancy and twenty 'cases' (16 per cent) at six weeks after birth. Postnatal affective disorder, which accounted for 15 of these cases, was significantly associated with dissatisfaction with the marital relationship and also with previous psychiatric history. The implications of the term 'postnatal depression' are considered in terms of the course of the disorder in the 29 women (23 per cent) who had episodes of affective disorder at some time during pregnancy and the postnatal year. We found that the majority of episodes of affective disorder could be understood in terms of previous psychiatric history and/or reaction to life-events, including the stress of childbirth itself.