The literature on hemifacial spasm and its surgical therapy is reviewed, and the authors' experiences with 20 patients are described. Vascular cross compression of the facial nerve adjacent to the brain stem is seen in 90% of the surgical patients. Mobilizing the offending vessel will cure or significantly improve approximately 80% of the patients. Complications occur in 25% of the patients and usually involve decreased hearing or facial weakness. Mortality is virtually zero, and this operation is vastly superior to any other medical or surgical therapy for hemifacial spasm. The pathophysiology is not yet understood.