Few studies have assessed the familiality of clinical characteristics in schizophrenia. Therefore, we set out to investigate the familiality of the following characteristics; age of onset, course of disorder, employment status at onset, impairment during disorder, marital status at onset, mode of onset and premorbid functioning. Clinical characteristics were recorded using the Operational Criteria Checklist for Psychotic Illness for 155 subjects with an RDC diagnosis of schizophrenia, schizoaffective disorder, or psychosis of unknown origin, from 61 families multiply affected by schizophrenia. Age of onset, course of disorder, impairment during disorder, mode of onset, and premorbid functioning were shown to be familial. The familiality of these clinical characteristics supports their use in the delineation of homogeneous subsets for future genetic studies.