Psychiatric illness in first-degree relatives of patients with paranoid psychosis, schizophrenia and medical illness.

This study examines the respective morbid risk for psychiatric illness determined by the family history method in the first-degree relatives of medical controls and patients with delusional disorder (paranoid psychosis) and schizophrenia. The morbid risk for schizophrenia and schizoid-schizotypal personality disorder was significantly greater in the relatives of the schizophrenic patients than in those of the delusional disorder or medical control patients, but no difference in the risk for affective illness or alcoholism was found in the three groups of relatives. Paranoid personality disorder was significantly more common in the relatives of the delusional disorder patients than in those of the medical controls. These results support the familial independence of delusional disorder and schizophrenia.