This case report presents a middle-ear osteoma mimicking otosclerosis that was located at the promontory. The osteoma was successfully excised using an endoscopic transcanal approach without any complication.

A 21-year-old man presented with a 4-year history of progressive conductive hearing loss (47 dB with a 30-dB air–bone gap) with intermittent tinnitus of recent onset in his right ear. Endoscopic transcanal middle-ear exploration showed that an osteoma located on the promontory was restricting the mobility of the stapes by affecting the anterior crus of the stapes. After transcanal resection of the osteoma, pure tone audiometry improved to 23 dB with a 5-dB air–bone gap. Tinnitus resolved spontaneously without any additional treatment.

Promontory osteomas, a rare and usually asymptomatic clinical entity, should be taken into consideration in the differential diagnosis in patients with progressive conductive hearing loss and tinnitus with intact stapedial reflexes and normal otoscopic findings.