Facial nerve (FN) function preservation is the primary goal during vestibular schwannoma (VS) resection. Many factors are linked to postoperative FN outcomes. This study evaluated the association between FN length and VS surgical outcomes. We included 70 consecutive patients who underwent VS microsurgery between October 2019 and November 2020. Clinical data was prospectively obtained from patients. Relative FN (rFN) length was obtained by subtracting the contralateral FN length from the ipsilateral FN length as measured by using DSI-Studio software. Postoperative FN function was HB Grade I in 67.1% (47/70), Grade II in 14.3% (10/70), and Grade III in 18.6% (13/70) of patients. Gross-total resection (GTR) was performed in 61 cases (87.1%). A residual tumor was retained to preserve FN function in 9 of 70 cases (12.9%), and rFN length was measured (mean diameter, 20.8 mm [range, 2.5-51.5]). On multivariate analysis, rFN length was significantly associated with the extent of tumor resection. The receiver operating characteristic curve indicated that the cutoff value for rFN length to predict intraoperative near-total resection (NTR) versus GTR was 36.6 mm, with specificity and sensitivity values of 93.4% and 88.9%, respectively. rFN length is important for predicting surgical outcomes. An rFN length >36.6 mm may indicate difficulty in achieving GTR for preserving FN function. Therefore, rFN length may become an objective indicator for neurosurgeons to predict the difficulty of GTR to preserve FN function. Copyright © 2021. Published by Elsevier Inc.