The aim of this study was to investigate cochlear functions in patients with ankylosing spondilitis (AS). Prospective, case control study. Twenty-eight AS patients (56 ears) and 25 healthy control subjects (50 ears) were included in the study. Pure-tone audiometry at 250, 500, 1,000, 2,000, 4,000, 6,000 Hz and immittance measures including tympanometry and acoustic reflex and DPOAEs (Distortion Product Otoacoustic Emission) testing were performed in the patients and controls. Pure-tone audiometry findings of the patients and controls were significantly different in all frequencies (P < 0.05). Sensorineural hearing loss was found in 10 patients (35%) that was bilateral in seven and unilateral in three patients. On DPOAE testing, there was no statistically significant difference between the levels of noise floor of the patients and controls (P > 0.05). However, the DPOAE responses of the patients and controls were significantly different in 3,000, 4,000, 5,000 and 6,000 Hz frequencies (P < 0.05). There is a damage of outer hair cells in patients with AS, and damaged outer hair cell regions mostly corresponds to the basal and mid-portions of the cochlea.