Acute hemiballismus after carotid endarterectomy--a case report.

A 72-year-old woman who experienced a postoperative stroke after a carotid endarterectomy with the presenting symptom of hemiballismus is described. This unusual presentation was likely the result of a hypotensive episode coupled with a predisposing anatomic variant in the circle of Willis, which compromised blood flow in the posterior cerebral circulation. She responded well to treatment with haloperidol with complete resolution of hemiballistic movements.