A 73-year-old woman had progressive right hemiparesis, aphasia, and focal motor seizures. EEG showed periodic discharges on the left. She died 8 weeks after onset. At autopsy, there was marked spongiform change, neuronal loss, and severe proliferation of astrocytes predominantly on the left and most prominently in the insular and centroparietal cortex. The changes were consistent with Creutzfeldt-Jakob disease (CJD), but pathology was slight or absent on the right side. This case appears as the first report of what might be called unilateral CJD. Such a condition should be included within the differential diagnosis of progressive unilateral cerebral disorders.