The genetic and clinical characteristics of 55 patients with schizophrenia and 138 control patients (with major psychiatric disorders), were studied in relation to the season of birth. The morbid risk (MR) of schizophrenia was significantly higher among relatives of the schizophrenic probands born in Spring than among those of the psychiatric controls born in the same season. The MR of schizophrenia was also significantly higher among relatives of schizophrenic probands born in Winter or Spring (6.9%) than in those of schizophrenic probands born in Summer or Autumn (0%). Among the schizophrenic cases, Winter births were marginally related to the paranoid subtype, whereas other clinical variables showed no clear relationship with the season of birth.