Introduction: Congenital cholesteatoma is a rare disease, usually presenting as an otoscopic or surgical finding. Objective: To report a case of a congenital cholesteatoma diagnosed due to an episode of acute mastoiditis, considering the etiology, clinical findings, diagnosis and treatment. Case report: A patient presenting signs of acute mastoiditis in the right ear and hearing loss, without otorrhea. Computed tomography suggested the presence of a cholesteatoma destroying the posterior limits of the temporal bone. A radical mastoidectomy was performed with total removal of the mass, which hystological examination revealed a congenital cholesteatoma. Conclusions: The existence of a congenital cholesteatoma should be evaluated in the presence of acute mastoiditis.