This report describes a case of hyperplasia of the mandibular coronoid process treated by coronoidotomy. A 26-year-old man visited our clinic complaining of restricted mouth opening. Panoramic radiography revealed marked hyperplasia of the right mandibular coronoid process. Three-dimensional CT showed that the coronoid process touched the temporal surface of the zygomatic bone at the maximal mouth opening position. His maximum mouth opening range was 27mm. The coronoid process was amputated about 8mm in width, and mouth opening training was done for a year after the surgery. Although the coronoid process and mandibular ramus reunited, the maximum mouth opening range was maintained at 40mm 13 months after the surgery.
