We present a case of adult onset progressive neurodegenerative disease with a selective involvement in the globus pallidus (GP). The main symptom was extreme slowness in motion without rigidity, which was distinct from akinesia of parkinsonism. Dystonic posture developed in neck and fingers and mild rigidospasticity appeared in a later stage. Neuropathological examination shows a selective neuronal loss with gliosis in GP and degeneration of the efferent fibers. Although the subthalamic nucleus is slightly atrophic with minimal gliosis, there is no neuronal loss in the nucleus. The rest of the structures are pathologically insignificant. Because the pathological change is confined to GP neurons and their efferent fibers, we think that the marked slowness in motion and dystonic posture are ascribable to the selective GP lesion. A degenerative neurological disorder preferentially involved in GP was reported as pure pallidal degeneration (PPD). The onset of the PPD was in the first or second decades and the main symptoms were choreoathetosis, torsion dystonia and progressive rigidity. These distinct clinical features seemed to distinguish the present case from the previously described PPD. Therefore, we would like to call our case "adult onset" PPD. Clinicopathological correlation is discussed.