Approximately 50% of patients with Parkinson's disease experience clinical depression. Neurotransmitter deficits in depression and Parkinson's disease suggest a common lesion may be responsible for this high incidence. In addition to similar psychological profiles, the clinical features of Parkinson's disease and depression likewise overlap making the distinction difficult. Differentiating these two diseases is very important, as each is treatable. The neuroscience nurse is in a unique position to evaluate the patient with Parkinson's disease for signs and symptoms of depression.