The Finnish adoptive family study of schizophrenia.

A nationwide Finnish sample of index offspring given up for adoption by schizophrenic women has been compared blindly with matched controls, that is, adopted-away offspring of nonschizophrenic biologic parents. The adoptive families have been investigated directly by joint and individual interviews and psychological tests. Interviewing and testing of biologic parents is in progress. In the total sample, thus far examined, of 124 index offspring, 9 (7.3%) have become psychotic; of 147 control offspring, 2 (1.4%) have become psychotic.