Pre-morbid schizoid and schizotypal traits and social adjustment were assessed blind to diagnosis by interviewing the mothers of 73 consecutively admitted patients with DSM-III schizophrenia or affective psychosis. Analysis of factors associated with pre-morbid deficits showed a highly significant interaction of diagnosis with sex, such that schizophrenic men showed much greater pre-morbid impairment than either schizophrenic women or men with affective disorder. Poor pre-morbid adjustment predicted an early age at first admission. The results can be explained by a neurodevelopmental disorder in some schizophrenic males.