Patients with otosclerosis were tested with pure tone and speech audiometry before and after stapedectomy. Also preoperative tests with hearing aids were done. At evaluation of these audiograms it was found that, in cases with mild or medium otosclerotic perceptive hearing loss, the operative gain was superior to the effect of a hearing aid. With severe inner ear damage the effect of stapedectomy and hearing aids seemed to be equal. In these cases, as well as in those with a relapse of the operative gain, unsuccessful stapedectomies or in border line cases, we used preoperative hearing tests successfully to provide additional information on inner ear function. In severe combined hearing loss, stapedectomy may improve the acoustic situation in view of the adaptation of a useful hearing-aid.