A family had a polymorphous neurological syndrome transmitted in autosomal dominant fashion. The clinical syndrome is one of late onset cerebellar ataxia, muscular rigidity, bradykinesia, dysarthria, fasciculations, muscle atrophy, and spasticity appearing in various combinations in affected individuals. Pathological studies on one case have revealed degeneration in spinocerebellar tracts, Purkinje cells and dentate nuclei of cerebellum, dorsal root ganglion cells, and cauda equina nerve roots. Peripheral neuropathy was present in several cases, as evidenced by demyelinating changes on sural nerve biopsy, and by characteristic changes in nerve conduction times and electromyography. Such changes on occasion preceded clinical signs of peripheral nerve disease. Several cases showed a therapeutic response to levodopa; only the symptom of rigidity was alleviated.