Parkinsonism-dementia complex (PDC) is the second most common neurodegenerative disorder in Guam, after amyotrophic lateral sclerosis (ALS). PDC was first described by Hirano 1961. A familial appearance is seen among some PDC cases, which may also include ALS, and vice versa, but subsequent research including pedigree analysis, prospective case control registries, and the search for specific gene markers has failed to yield a satisfactory genetic explanation. Important diagnostic indicators of the illness include rigido-akinetic type Parkinsonism and severe dementia.In PDC, rigidity is so marked that postural deformities such as a generally flexed posture become rather prominent. Gait disturbances are a common initial symptom. Hyperreflexia and spinal muscular atrophy, developing mainly in the distal extremities, are frequently observed. These mixed-syndrome patients can be seen as clear support for the view that Guam ALS and PDC constitute a single mixed disease entity with a spectrum of clinical expression. The present paper offers an overview and description of the clinical features of PDC.