A 71-year-old right-handed man noted the insidious onset of balance abnormalities 9 months prior to his initial admission at a local community hospital. During that time, he also exhibited slurred speech and unusual behaviors, including violent outbursts. The patient's gait abnormalities worsened more rapidly over the 5 months immediately preceding his initial hospitalization, and he endured numerous falls despite using a cane. Two months prior to his hospitalization, he experienced daily nausea with vomiting and visual difficulties followed by a further precipitous decline in his functional status. At the time of his first admission, the patient's family reported that his thoughts were so disorganized that he was unable to maintain a cohesive conversation. Additionally, they noted that he had not been able to stand or sit independently for the previous 6 to 8 weeks, and had nearly constant involuntary flinging movements of his arms, legs, and trunk. Because of these motor difficulties and mental changes, he required assistance with feeding, dressing, and his daily hygiene. He was evaluated by a local neurologist who prescribed haloperidol up to 12 mg/day, which resulted in partial control of the involuntary movements and aggressive outbursts. On transfer to the university hospital, his medications included haloperidol, diltiazem, furosemide, potassium chloride, nitropaste, isosorbide, aspirin, and omeprazole. The patient had not received any other medications during the previous year.His medical history was significant for insulin-dependent diabetes, hypertension, congestive heart failure, and emphy-A videotape accompanies this article.