From January 1990 to December 1996, 293 primary stapedectomies for otosclerosis were performed, among which 14 had obliterative otosclerosis (4.7 per cent). Probability of bilateral obliterative disease was 50 per cent. With this particular condition, a drill-out procedure was used to perform either a stapedectomy or a stapedotomy. In two patients with bilateral ‘far-advanced otosclerosis’, surgery was effective in enabling the patient to benefit from hearing-aids. In patients with a measurable hearing-loss, an air-bone gap closure to within 10 dB was achieved in 62.5 per cent of the cases and to within 10–20 dB in 37.5 per cent of the cases, with no deterioration of air-conduction thresholds at 8 kHz. A mild sensorineural hearing loss at 4 kHz was observed in 25 per cent of the cases. There was no statistical difference between stapedectomy and stapedotomy. According to these results, the drill-out technique is a safe and effective procedure in cases of obliterative otosclerosis.