Sensorineural hearing loss has been reported in various autoimmune diseases. The relationship between Hashimoto's thyroiditis (HT) and the auditory system has not been previously evaluated. In this study, we investigated the effect of euthyroid HT on the hearing ability of adult patients. The study included 30 patients with newly diagnosed euthyroid HT and 30 age- and gender-matched healthy controls. All subjects had a normal otoscopic examination and tympanometry, and they were negative for rheumatoid factor, antinuclear, anti-smooth muscle, antimitochondrial, antineutrophilcytoplasmic, and antigliadin antibodies. Pure tone audiometry exams at 250, 500, 1000, 2000, 4000, 6000, and 8000 Hertz (Hz) were performed in both groups. Thyroid peroxidase antibody and thyroglobulin antibody (anti-Tg) levels were higher in HT group while TSH, free T4, free T3, plasma electrolytes, glucose, lipid profile, vitamin B12, and blood pressure measurements were similar between the two groups. Higher audiometric thresholds and a higher prevalence of hearing loss at 250, 500, and 6000 Hz were detected in the HT patients than in the healthy controls (P < 0.05). Hearing levels at 250 and 500 Hz correlated positively with anti-Tg levels (rho = 0.650, P = 0.002; rho = 0.719, P < 0.001, respectively), and this association remained significant in linear regression analysis. Anti-Tg-positive HT patients had higher hearing thresholds at 250 and 500 Hz than anti-Tg-negative HT patients. Hearing thresholds were similar between anti-Tg-negative HT patients and the control subjects. This study demonstrated that hearing functions are impaired in HT patients. Thyroid autoimmunity seems to have an important impact on a decreased hearing ability, particularly at lower frequencies, in this population of patients.