A 27-year-old man presented with a sporadic, nonprogressive, right-sided, segmental movement disorder that had started at the age of 2 years. Ballistic movement overflow myoclonus was diagnosed clinically and by surface electromyography. Special investigations did not detect anything except atrophy of the left temporal lobe on CT scan. The movement intensity was attenuated by alcohol but was minimally affected by high doses of oral propranolol (320 mg daily), clonazepam (36 mg daily), or trihexyphenidyl (32 mg daily). High-dose intravenous biperidine (10 mg) resulted in dramatic improvement, but with unacceptable side effects. The possible role of a cholinergic disturbance in generating myoclonus is discussed.