Familial Creutzfeldt-Jakob disease without periodic EEG activity. Four members of a kindred with Creutzfeldt-Jakob disease are reported, in whom myoclonus did not develop and in whom serial electroencephalograms performed late in their illness failed to show periodic sharp wave complexes. Otherwise, the patients' disease duration, clinical features, and neuropathological findings were similar to those described in sporadic cases of Creutzfeldt-Jakob disease. Our findings and those reported by others suggest that periodic electroencephalographic activity may be rare in familial forms of Creutzfeldt-Jakob disease, as it is in other slow transmissible encephalopathies. 