Adenomas of the middle ear are rare benign glandular neoplasms arising from the middle ear mucosa. After previous operations 25 and 15 years before, a 67-year-old female complained about dizziness, tinnitus, and unilateral hearing loss on the left side. A tumor in the tympanum that was revealed by otoscopy could be removed completely. Histological examinations showed an adenoma of the middle ear with cholesteatoma. This was inconsistent with the histological result of the operation in 1983, which had described a hidradenoma. An exact analysis of the preparations confirmed that a middle ear adenoma had already been present in 1983. Hidradenoma is one of the most important differential diagnoses. The characteristic histological sign of middle ear adenomas in contrast to hidradenomas is the lack of myoepithelial cells. In addition, it is very difficult to differentiate middle ear adenoma and adenocarcinoma using histopathological and clinical methods. Therefore, thorough follow-up is mandatory for patients after surgical treatment of middle ear adenomas.