Background and Objectives: Idiopathic sudden sensorineural hearing loss (ISSHL) is a rapid loss of hearing, exceeding 30 dB in at least 3 consecutive frequencies within 3 days, without any identifiable cause despite thorough investigations. Currently, the etiology and pathogenesis of ISSHL have not been fully elucidated. This study aimed to assess the size of the cochlear nerve in patients with ISSHL and explore its relationship with pretreatment audiograms and treatment response. Subjects and Methods: A total of 125 patients (59 [47.2%] women; mean age 47.7±13.8 years [minimum-maximum: 21-76]) and 60 healthy participants (27 [45%] women; mean age 45.7±16.8 years [minimum-maximum: 20-76]) as a control group were included in this study. The size of the cochlear nerve was assessed on the affected side, compared to the control group, as well as on the unaffected side. Pretreatment and posttreatment audiological values were also analyzed. Results: The cross-sectional area (CSA), vertical diameter (VD), and horizontal diameter (HD) of the CN were found to be smaller on the affected side of ISSHL patients compared to the control group (p<0.01; p=0.04; p=0.02, respectively). In the study group (affected side of ISSHL patients), there were no significant differences in VD, HD, and CSA values between pretreatment audiogram types (p=0.23; p=0.53; p=0.39, respectively), and initial hearing levels (p=0.16; p=0.22; p=0.23, respectively). Furthermore, there were no significant differences in VD, HD, and CSA values between the recovery groups according to Furuhashi criteria (p=0.18; p=0.37; p=0.27, respectively). Conclusions The size of the CN may be a risk factor for ISSHL, but it does not affect the type of audiogram curves and was not prognostic in terms of treatment response.