Study of chronic schizophrenics with positive and negative family histories of psychosis.

We found no differences in clinical symptoms among chronic schizophrenics with a family history of psychosis (n = 18) and without any affected relatives (n = 22). The lifetime morbidity risks of psychosis in the former group were 0.59 +/- 0.13 for children and 0.33 +/- 0.07 for siblings.