OBJECTIVE: To report an extremely rare case of congenital cholesteatoma (CC) of the mastoid region. The mastoid process is the least frequent occurrence site, with only a small number of cases reported worldwide. CASE REPORT: A 45-year-old woman presented with a 7-month history of recurrent episodes of nonspecific dizziness, self-limited, lasting for a few minutes with gradual progression. At the same time, she had complaints of uninterrupted tinnitus on the left side characterized by a thin whistling sound. She had no prior ear infection, trauma, or hearing loss. Physical examination revealed normal tympanic membranes without perforation or retraction in both ears. Computed tomography (CT) and magnetic resonance imaging (MRI) of the temporal bone showed a large, dense, soft-tissue-density lesion occupying the posterior portion of the mastoid process, which had eroded only the bony plate of the posterior fossa. MRI revealed a diffusion restriction. Cerebral angiography showed no tumor perfusion. Audiometric examination, impedance, and caloric tests were normal. During surgery (transtemporal approach), the mastoid was found to be filled with cholesteatoma, which had almost completely destroyed the posterior fossa bony plate and the bony plate covering the sigmoid sinus. The disease was completely removed. The middle ear, attic, aditus ad antrum, and the antrum were unaffected. It was not possible to establish a relationship between the patient's symptoms and the lesion. CONCLUSION: Congenital mastoid cholesteatoma has a variable presentation, the most common being an incidental finding, as described in our report. Therefore, imaging remains as the main diagnostic method.