The hypothesis that schizophrenic men have a lower familial risk for schizophrenia than schizophrenic women was tested using the DSM–III-diagnosed samples of the Iowa 500 and non-500 family studies. Survival analyses were used to test for differences in the risk for schizophrenia and spectrum disorders, for sex of proband and sex of relative, controlled for fertility effects and ascertainment bias. Male and female relatives of schizophrenic men had a significantly lower risk for schizophrenia, schizophreniform, and schizoaffective disorders than relatives of schizophrenic women. However, the effect was not significant for the full spectrum nor when analysed by sex of relative. Sex differences in the risk for other psychiatric disorders among relatives of schizophrenic probands were not significant.