Postnatal depression (PND) has been underreported in South Africa. This retrospective study investigated factors which appear to predispose women to PND. Two groups, one consisting of women who suffered from PND and the other of women free of this complaint, provided information on a number of biological, psychological and social factors. In line with current opinion it was found that no single causative factor could be isolated but that a variety of factors may contribute to the problem. Among the factors which distinguished the two groups were the mothers' emotional health during pregnancy, complications after birth, marital relations, relationship with their own mothers, social support and preparation for motherhood. An alarming finding was that a large proportion of the PND sufferers had not known of the disorder's existence before their own diagnosis.