A 64-year-old man presented with a three day history of progressive Broca's aphasia, followed within 3 weeks by exclusively right-sided myoclonus, rigidity, and dystonia. Within 4 weeks he was globally aphasic. He died within 7 weeks of onset. In the final week, rigidity and myoclonus became bilateral. CT and MRI were normal. SPECT showed diminished perfusion of the left hemisphere. EEG showed periodic discharges on the left. At autopsy, there were marked cortical spongiform change, neuronal loss, and gliosis throughout the left hemisphere and in the right occipital cortex. Elsewhere in the right hemisphere, spongiform change was non-existent to minimal. There was moderate spongiform change in the molecular layer of the cerebellar cortex, much more marked on the left. Clinical and pathological unilateral cerebral predominance extended to the ipsilateral cerebellum. Creutzfeldt-Jakob disease is an important consideration in patients with rapidly progressive unilateral cerebral signs associated with a movement disorder.