The age at onset of schizophrenia was investigated in 2,417 inpatients (1,433 males and 984 females) meeting the DSM-111 criteria for schizophrenia. About 80% of the patients became schizophrenic before the age of 30. The mean age at onset of the male patients was slightly earlier than that of the female patients. There was a higher cumulative percentage of the male patients who became affected at each age quinquennium. More men than women became schizophrenic before the age of 30.

Sex concordance rates were investigated in 278 schizophrenic probands, who had at least one first‐degree relative with schizophrenia, in order to find out whether the illness affects the same sex more often than the opposite sex when two close relatives become ill. No such unusual concordance rates were found in proband‐relative pairs with schizophrenia. When 118 of the 278 probands were examined who had at least one parent with schizophrenia, the morbidity risk for schizophrenia in siblings of the same sex as the schizophrenic probands was significantly higher than that found in siblings of the sex opposite that of schizophrenic probands.