The authors analysed the results of 300 microvascular decompression(MVD) procedures for hemifacial spasm. The follow up period ranged from 6months to 3years. Of these, 70% were women(mean age 54). The vessel most frequently found to compress the facial nerve was the posterior inferior cerebellar artery(43.3%) followed by anterior inferior cerebellar artery(26.7%). For the surgical results, 210 patients(70%) had complete relief of spasm within 3 days after MVD, 65 patients(21.7%) subsequently experienced complete relief, noted in 4 days to 6 months after MVD, ten patients had delayed partial relief and remaining 15 patients showed no improvement. Twelve patients of these 15 unresponsive patients underwent reoperation without beneficial results. Recently the authors have monitored facial elctromyography(EMG) intraoperatively to observe the abnormal late response. There were few cases of permanant major complications, including two cases of ipsilateral hearing loss, ataxia and no operation-related death. These results suggest that MVD is a safe and definite treatment for hemifacial spasm, if performed by experienced surgeon with gentle operative technique, and with intraoperative monitoring such as auditory evoked potential and facial EMG, better surgical results with less complications can be expected.