Thirty-three patients admitted to hospital with severe early onset puerperal psychiatric disorders were compared with matched normal puerperal controls. Interviews, which were administered after recovery, covered life events in the previous thirteen months and detailed assessment of previous and personal history, pregnancy and labour, other aspects of stress, social support, and marital relationships. No differences, except for previous history of psychiatric disorder, were found between patients and controls or between patients with depressive and with other diagnoses. These findings of absence of social stress contrast with previous studies of milder post-partum depression and of disorders with onset during pregnancy, and suggest that the aetiology of severe post-partum disorders is predominantly biological.