Hearing loss that may develop after radiotherapy for head and neck tumors are largely classified into conductive and sensorineural hearing losses. Middle ear inflammation or edema around the eustachian tube may cause conductive hearing loss. Although this complication may be unpleasant, it is transient and reversible. In contrast, the radiation damage to the inner ear may lead to sensorineural hearing loss, which is permanent and irreversible. In this study, we compared between pre-and post-irradiation bone conduction hearing levels in patients with head and neck malignancy, whose inner ear had been included in the radiation field. Thirty four ears of twenty patients have been investigated for 1 through 60 months following irradiation. Seven of 34 ears had hearing losses of more than 10dB. Sensorineural hearing loss was relatively increased when irradiation was performed at an old age. In contrast, no correlation was found among the total radiation dose, frequencies of audiometric test, follow-up duration and degree of hearing impairment. The possible harmful effect of irradiation on hearing should be kept in mind in planning treatment or in postirradiation follow-up.