Cholesteatoma of the maxillary sinus, also known as keratoma, primary epidermoid tumor, epidermoid cyst, and keratocyst, is a rare entity, with a clinical presentation and radiologic findings that are difficult to distinguish from those of malignancy. We report a case of cholesteatoma of the maxillary antrum that occurred in a 12-year-old boy without any history of predisposing factors. Multiple theories of pathogenesis have been proposed throughout history; currently there are two accepted ones. We discuss these theories and present, along with the differential diagnosis, a review of the literature and the characteristic radiologic and pathologic findings. While it is a rare entity, the diagnosis of cholesteatoma should be considered for any slowly expanding lesion of the maxillary antrum.