To evaluate the efficacy of the second operation within 1 week after ineffective microvascular decompression (MVD) for patients with primary hemifacial spasm (HFS), and to find out the causes of failure. The surgery records and postoperative follow-ups of 52 primary HFS patients who had poor relief of spasm after their first MVDs were investigated. Patients were divided into 2 groups. Group A included 46 patients (16 males and 30 females) that went through the second operation within 1 week after the failure of the first MVD. Group B included 6 patients (3 males and 3 females) which did not take the reoperation. The level of spasm of each patient was then re-evaluated 1 year after the first surgery. Among 52 patients who had poor relief after the first MVD between April 2016 and October 2019, 46 patients underwent a second MVD within 1 week while 6 patients refused to take the reoperation. Their mean duration of HFS was 102.4 ± 57.9 months. During reoperations for patients in group A, we discovered additional sites of neurovascular compression in 11 cases (23.91%). Forty-five patients (97.82%) in group A achieved complete relief 1 year after the second surgery while there was 1 recurrent case. Four patients (66.67%) in group B achieved delayed relief 1 year after the first surgery, while the other 2 patients were still suffering facial spasm in the 1-year follow-up. Group A demonstrated higher relief rate compared to group B in the 1 year follow up (P = 0.032). Although no severe complications occurred on patients in both group, 4 of them suffered grade II facial palsy, and another 3 patients had developed mild temporary hearing loss on the operation side. The second operation within 1 week after an ineffective MVD is safe and effective. Full revealing of root exit zone and making sure no neurovascular compression missed with abnormal muscle response monitoring are the keys to a successful MVD. Copyright © 2021 by Mutaz B. Habal, MD.