Parkinsonism is a clinical syndrome characterized by tremor, bradykinesia, rigidity, and postural instability. Parkinsonism shares symptoms found in Parkinson's disease, from which it is named; but parkinsonism is a symptom complex, and differs from Parkinson disease which is a progressive neurodegenerative illness. The underlying causes of parkinsonism are numerous, and diagnosis can be complex. The neurodegenerative condition Parkinson's disease (PD) is the most common cause of parkinsonism. However, a wide range of other etiologies may lead to a similar set of symptoms, including some toxins, a few metabolic diseases, and a handful of neurological conditions other than Parkinson's.