Hemifacial spasm, like tic douloureux and several other cranial nerve dysfunction syndromes, is a symptom caused by cross compression-distortion, usually arterial, of the appropriate nerve at the brainstem. Symptoms of disordered hyperactivity and mild loss of function can be reversed by microsurgical mobilization of the vessel away from the nerve. This appears to be a safe and definitive procedure, but it should be performed only by a trained microneurosurgeon with experience in the cerebellopontine angle.