Eighty-two mother–infant dyads, comprising women with psychiatric disorder andindividually matched controls, were followed up over the children's 1st year of life. Themothers with mental illness consisted of two subgroups: first, 25 severely mentally ill motherswho had been admitted to a psychiatric unit with their infants; and second, 16 mothers from acommunity sample meeting research diagnostic criteria for unipolar, nonpsychotic depression.With the exception of six dyads in the in-patient group, observations were made of themother–infant interaction and the quality of the infant–mother attachmentrelationship at 12 months. The nature and course of the mothers' illness was alsodocumented. Although few residual symptoms of maternal mental illness were detected at 1 yearpostpartum, interactional disturbances were evident among the case group dyads. A strongassociation was revealed between infant–mother attachment quality and maternaldiagnosis: a manic episode of illness in the postpartum period was related to security in theattachment relationship, and psychotic or nonpsychotic depression was related to insecurity.Concurrent patterns of mother–infant interaction provided support for this finding.