A pathologic, chronic inflammatory process characterized by the accumulation of keratinizing squamous epithelium, resulting in the accumulation of debris in the middle ear and/or mastoid. It may be congenital but is more commonly acquired. If left untreated, it may increase in size and destroy adjacent structures, resulting in hearing loss, facial paralysis, and less commonly, intracranial complications. Treatment is surgical removal. Patients who have had cholesteatoma removal surgery require lifelong monitoring of their ears for recurrence.