The annual incidence of sporadic Jakob-Creuzfeldt disease has been stable for the last 30 years. The new variant affecting young adults which appeared in the United Kingdom (20 cases) and France (1 case) in 1994 is due to the same infectious agent which causes bovine spongiform encephalopathy. Epidemiological data are still insufficient for a precise prediction of epidemics of the new variant mainly due to the duration of the incubation period of the disease.