Hearing loss has commonly been reported in association with thyroid disorders and during treatment with propylthiouracil. The relationship between hyperthyroidism and the auditory system has not been previously investigated. The aim of this cross-sectional, case-control study was to investigate hearing loss in patients with Graves' disease (GD). The study population consisted of patients with newly diagnosed GD and healthy controls. Pure tone audiometry at frequencies of 250, 500, 1000, 2000, 4000 and 8000 Hz, along with immittance measures including tympanometry and acoustic reflex tests, were performed in all participants. Twenty-two GD patients and 22 healthy controls consented to inclusion in the study. The differences between groups with regards to age and gender distribution were statistically insignificant (P = 0.567 and P = 0.757, respectively). The hearing thresholds of right and left ears were also similar in both groups (P > 0.05). When single-ear evaluations were taken into account (total of 44 ears for both groups), hearing thresholds in the GD group were significantly higher than healthy controls at all frequencies (P < 0.05). Following testing at the designated frequencies, the only significant effect of thyrotoxicosis was observed with frequencies of 4000 and 8000 Hz. The odds ratio for having hearing loss at a frequency of 8000 HZ associated with GD was 14.97 (95% confidence interval 4.03-55.64). In patients with GD, right and left pure tone audiometric findings at a frequency of 8000 Hz correlated positively with FT3, FT4 and negatively with TSH. Our results are highly suggestive of a decrease in hearing ability in patients with GD, particularly at high frequencies. Further studies are needed to help elucidate the mechanisms behind hearing loss which develops in association with GD.