The families of sixteen adolescent or young adult schizophrenics were intensively studied. Few of the twenty-six siblings of the patients could be regarded as reasonably well adjusted. In fact, the siblings could be equally divided into psychotic and fairly well integrated groups. The brothers of the male patients were more disturbed than their sisters; the sisters of the schizophrenic females were more disturbed than their brothers. The clinical material offers considerable understanding of why one child rather than another in a family becomes schizophrenic, and it supports the hypothesis that intrafamilial environment is of major importance in the etiology of schizophrenia.