Machado-Joseph disease is an autosomal dominant spinocerebellar degeneration. It expresses itself clinically with variable expression. Type one patients have early onset with a rapid progression of symptoms including spasticity, rigidity and myokymia. Type two patients are the most common phenotype with ataxia and spasticity. Type three patients develop progressive ataxia with variable amyotrophy. All patients have ophthalmoparesis and normal mental status. The neuropathology consists of neuronal loss and gliosis in the substantia nigra, motor cranial nuclei, dentate nucleus of the cerebellum, and variable neuronal loss with gliosis in the cerebellar cortex and neostriatum. The cerebral cortex is normal histologically. The inferior olivary nuclei are normal, thus separating this disease from olivopontocerebellar atrophy (OPCA). The disease has a worldwide distribution including families described in Portugal, the Azores, Spain, Italy, United States, Canada, Brazil, China, Taiwan, and Japan. The gene has not been mapped for this disease but the locus on chromosome 6p mapped for most families with OPCA has been excluded for this disorder.