An attempt was made to ascertain all cases of Creutzfeldt-Jakob disease occurring in England and Wales during the 5 year period 1980-1984. The mean annual mortality rate was 0.49/million; women were more frequently affected than men. The age-specific mortality rate reached a peak in the seventh decade. A case-control study involving 92 of the 122 definite and probable cases ascertained failed to confirm the reality of previously suspected aetiological agents in the environment. Although there was no confirmed instance of familial Creutzfeldt-Jakob disease in the case-control study, dementia in close relatives was significantly more common than in controls.