Parkinson's disease is a progressive neurologic disorder without cure. About 1% of the US population over 50 years of age is afflicted. Loss of dopaminergic neurons originating in the substantia nigra is the typical pathologic feature. It is theorized that both genetic and environmental factors have a role in the etiology of the disease. The classic tetrad of parkinsonian signs includes tremor, rigidity, bradykinesia, and disturbances in posture and gait. Initial signs and symptoms can be subtle and nonspecific. As the disease progresses, vocal, neurologic, autonomic, and psychiatric complications may develop. Mortality rates have not changed in 30 years despite new therapy. Differentiating true Parkinson's disease from other causes of parkinsonism can be challenging but is crucial to outcome.