A cholesterol granuloma of the petrous bone is an expanding mass which contains fluids, lipids, chronic inflammatory cells, and cholesterol crystals surrounded by a fibrous lining. The goal of surgery is to provide drainage and ventilation of the affected area to prevent recurrences. In this article, we report a case of a 27-year-old man who was operated using the transmastoid infralabyrinthine approach to drain a cholesterol granuloma cyst.