OBJECTIVE: Intraoperative abnormal muscle response (AMR) monitoring is used as an indicator of postoperative outcome in patients with hemifacial spasm (HFS). We investigated whether AMR findings influence manipulation of microvascular decompression and improve the postoperative results. MATERIALS AND METHODS: Subjects were 102 HFS patients who underwent AMR monitoring during surgery. The value of AMR monitoring was classified into four categories: a guiding, a confirming, an indirect confirming, or an inconclusive role. The relationship between AMR monitoring results and surgical outcome was analyzed. RESULTS: The overall cure rate was 92.2%. A guiding role of AMR monitoring was apparent in 13.7% of patients, and a confirming role was demonstrated in 53.9% of patients. The cure rate was 92.9% in patients defined as guiding, and 96.4% in patients defined as confirming cases. When the AMR remained disappearance until completion of decompression in patients assigned in indirect confirming, 13 of 15 patients (86.7%) experienced resolution postoperatively. In patients defined as inconclusive cases, 14 of 16 patients (87.5%) in whom AMR still presented but its amplitude decreased at the end of surgery experienced complete resolution. CONCLUSIONS: This study demonstrates that meticulous evaluation of AMR findings intraoperatively can help to improve the results of surgery. We believe that intraoperative AMR monitoring is useful in microvascular decompression for HFS.