Two hundred and sixty seven patients with a definite or probable diagnosis of Creutzfeldt-Jakob disease (CJD) were identified in an attempt to ascertain all cases of the disease in England and Wales in the period 1970-84. No evidence of space-time clustering of dates and places of onset was found for these cases. Two age- and sex-matched controls were selected for 72 of the 122 cases diagnosed in the period 1980-84 and life histories of places of residence were obtained for these cases and the controls. No evidence was found that cases had lived closer to each other than had controls at any time in their lives, except that there was an excess of cases born in London. The study does not provide supportive evidence for case-to-case transmission of CJD being an important component in the aetiology of the disease.