A variety of neuropharmacologic agents, including anticholinergic drugs, amantadine hydrochloride, levodopa, selegiline, bromocriptine, and pergolide, are now available for the treatment of Parkinson's disease. Of patients treated with dopaminergic agents, 30% develop visual hallucinations, 10% exhibit delusions, 10% have euphoria, 1% have mania, 10% to 15% experience increased anxiety, 15% have confusional periods, and a few exhibit altered sexual behavior. Anticholinergic drugs have a greater tendency to produce confusional states than dopaminergic compounds. Elderly patients and those with underlying dementia are most likely to have untoward side effects with anti-parkinsonism treatment. Dosage reduction is the optimum management strategy, although anti-psychotic agents may be necessary in patients with delusions, and lithium may help control drug-induced mania. Dopaminergic agents share the property of stimulation of D2 dopamine receptors, and this action may play an essential role in mediating their neuropsychiatric effects.