The Influence of Metabolic Syndrome on the Prognosis of Idiopathic Sudden Sensorineural Hearing Loss Objectives: We aimed to verify the hypothesis that metabolic syndrome (MetS) and its components affect the prognosis of idiopathic sudden sensorineural hearing loss (ISNNHL). Study Design: A retrospective cohort study. Setting: Tertiary otology referral center. Patients: We divided patients who were diagnosed with ISSNHL between January 2015 and January 2018 into a MetS group and a Non-MetS group according to the diagnostic criteria of MetS. Interventions: We diagnosed ISSNHL patients by using pure-tone audiometry and treated them with oral steroids, blood flow promoting agents, and hyperbaric oxygen therapy. Main Outcome Measures: We used multivariate logistic analysis to identify prognostic factors of ISSNHL. Results: The MetS group comprised 94 patients, and the Non-MetS group comprised 162 subjects. Despite the rate of hypertension, diabetes mellitus, hyperlipidemia, and BMI, no significant difference was observed between the two groups (p > 0.05). The rates of complete recovery and partial recovery of the MetS group were significantly lower than those of the Non-MetS group (p < 0.05). According to the multivariate analysis, MetS was significantly correlated with a poor prognosis (OR = 2.912, p = 0.008), and the OR increased with an increase in the number of MetS components. Late onset of treatment, high initial hearing threshold, and presence of diabetes mellitus and hyperlipidemia were associated with a poor prognosis (p < 0.05). Conclusions: The presence of MetS may negatively affect the recovery of Chinese patients with ISSNHL, and the prognosis was poorer with an increase in the number of MetS components. Early onset of treatment, low initial hearing threshold and absence of diabetes mellitus, and hyperlipidemia are associated with favorable hearing recovery. Address correspondence and reprint requests to Hong Sun, M.D., Ph.D., Department of Otolaryngology Head and Neck Surgery, Xiangya Hospital of Central South University, Xiangya Road 87, Changsha 410008, Hunan, China; E-mail: shjhaj@126.com Data collection: Q.J. and S.X. Data analysis and draft writing: Y.Z. Technical and material support: X.W. and Y.F. Study design and supervision: H.S. Research was funded by the National Key Basic Research Program of China (No. 2014CB943003), Natural Science Foundation of Hunan Province (No. 2018JJ3842), and the Fundamental Research Funds for the Central Universities of Central South University (No. 2017zzts236). The authors disclose no conflicts of interest. Copyright © 2019 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company