We diagnosed Cruetzfeldt-Jakob disease in 34 patients (16 definite, 18 probable) who had received human growth hormone extract for various period of time (mean +/- SD, 2.9 years), but particularly during the period between January 1984 and July 1985, a potential high-risk factor. Disease duration for deceased patients (n = 30) was 17 +/- 9 months. The clinical picture was homogeneous, starting with cerebellar ataxia and ocular motor disorders in about 90% of the patients. Neurologic deterioration, including dementia and myoclonic jerks, occurred within months. The high number of cases (1.5% of those treated between 1959 and 1988, 3% of those treated during the putative high-risk period) is still unexplained. We discuss the possibility that new cases will be detected,the risk of contaminating the general public, and the sanitary measures undertaken to prevent this.