Patients with head and neck cancer after radiotherapy often suffer disability such as hearing disorders. In this study, the effect of radiotherapy (RT) on hearing function of patients with head and neck cancer after RT was determined according to the total dose delivered to specific parts of the auditory system. A total of 66 patients treated with primary or postoperative radiation therapy for various cancers in the head and neck region were selected. All patients had audiologic evaluation with pure tone audiometry for the frequencies of 250, 500, 1,000, 2,000, 3,000, 4,000, 6,000, and 8,000 Hz before and immediately after completion of treatment and again 3 months later. The cochlea dose volume histograms of the patients were derived from their computed-tomography-based treatment plans. At study's end, RT-induced auditory complications developed in 33% of patients. The greatest hearing loss (changes >15 dB) occurred immediately after RT at frequencies of 3,000 (14.5%), 4,000 (12.9%), 6,000 (13.6%), and 8,000 Hz (10.6%), and after 3 months of follow-up, at 3,000 (6.8%), 4,000 (7.7%), 6,000 (10.7%), and 8,000 Hz (12.1%). Univariate and multivariate analyses indicated a positive relationship between dose delivered to the cochlea and hearing loss (p < 0.001, r = 0.484). An increased risk of hearing loss was present for patients receiving ≥40 Gy as their mean dose compared with those receiving <30 Gy. We conclude that radiation dose has negative effects on the auditory system. This effect occurs more in high-frequency hearing. The received dose to the cochlea was the main cause of damage to hearing.