A 20-year follow-up was done on a patient with a large congenital cholesteatoma of the petrous apex. The patient was treated successfully with marsupialization through a radical mastoidectomy and sphenoid sinusotomy. Cranial computed tomography and magnetic resonance imaging demonstrated continued cholesteatoma growth. Bone-conduction thresholds remained normal despite replacement of the internal auditory canal by cholesteatoma matrix. The patient continues to have chronic otorrhea, but is otherwise asymptomatic.