Descriptive epidemiological data are presented from a survey of 35 cases of Creutzfeldt-Jakob disease (CJD) that occurred in Chile in the period 1955 to 1977. The average annual mortality in Chile (0.31 deaths per 1 million) and in urban Santiago (0.73 deaths per 1 million) is compared with data reported from other countries. An increasing incidence in recent years is probably related to a greater awareness of the disease. The familial occurrence of CJD in nine patients from five affected families is described, and its analysis suggests a genetically determined susceptibility with incubation periods of more than 30 years. Horizontal transmission of the disease may have occurred in one patient in whom the disease developed 13 years after the patient married into a family with seven other affected members.