Congenital cholesteatoma(CC) accounts for 2-5% of all cholesteatomas most common site being middle ear. We report an extreme-ly rare case of congenital cholesteatoma iso-lated to the mastoid process, with no middle ear involvement. An 18 year old male pre-sented with ear ache and minimal discharge for 4 months. On examination, external audi-tory canal was found narrowed with granula-tions and bony defect present in the postero-inferior part of canal. Computed tomography showed soft tissue contents in the mastoid bone causing full thickness erosion of the same along with attenuation of ear canal. At surgery, a large cholesteatoma sac was found within the mastoid process completely eroding it and extending to posterior part of external auditory canal. The mastoid antrum and aditus were found normal. Tympanic membrane was intact. CC isolated to the mastoid was diag-nosed. Diagnosis of CC isolated to the mastoid should be based on clinical examination and radiological evaluation.