The annual incidence of sporadic Jakob-Creuzfeldt disease has been sta
ble for the last 30 years. The new variant affecting young adults whic
h appeared in the United Kingdom (20 cases) and France (1 case) in 199
4 is due to the same infectious agent which causes bovine spongiform e
ncephalopathy. Epidemiological data are still insufficient for a preci
se prediction of epidemics of the new valiant mainly due to the durati
on of the incubation period of the disease.