Two cases of osteochondroma of the coronoid processes of the mandible are presented because of the rarity of reports of this condition, because the diagnosis is so easily missed on routine roentgenography, and because, with awareness of the condition and proper films, a disabling condition may be cured by simple surgical means. Case I (Figs.1–4): C. H. P., a 30-year-old white male in no distress, well nourished and well developed, complained only of inability to open his mouth normally. He had first experienced difficulty at the age of fourteen and it had grown progressively worse. No pain was ever present in the temporal region. There was no history of trauma. Examination at two or more hospitals had led to a diagnosis of arthritis involving the temporomandibular joints. The only significant finding on physical examination was inability to open the mouth more than 7mm. A forcible attempt at wider opening was unsuccessful. Laboratory studies were negative. Roentgenograms were interpreted as showing hyperplasia of the coronoid processes with exostoses of the zygomata at the point of contact. On Dec. 21, 1953, under Xylocaine anesthesia, an intraoral exploration was performed and the coronoids were palpated with difficulty. There was a mild infection following this, and definitive therapy was postponed until Jan. 22, 1954, when a right coronoidectomy was performed. Immediately the space between the teeth could be increased to 1.2 cm., although there was now lateral deviation. On Feb. 4, a left coronoidectomy was performed and immediately the patient could separate the teeth by 1.7 cm. He was sent on leave, with exercises prescribed, and on his return to be discharged he could open his jaws to 2.8 cm. On Jan. 4, 1955, the patient was seen by the surgeon, Capt. William Van Zile, and had full ability to open his mouth. There were no other complaints. Operative specimens were reported by the pathologist, Dr. M. S. Bowman, as consisting of compact bone from the coronoids and exostoses of the zygoma. Thoma (1) believes that these start as osteochondromata since they develop at a surface where there is a tendinous attachment, usually beginning at approximately fourteen years of age. No chondromatous element was apparent in the removed specimen in this case. Despite this lack, the diagnosis of osteochondroma was considered correct according to the clinical history. Case II (Figs.5 and 6): A. R., a 36-year-old man in no acute distress, complained only of inability to open his mouth. At the age of thirteen he had fallen and sustained a cut on the chin, but the present complaint did not develop until a year later. It had grown progressively worse. Examination on two previous occasions had not resulted in a clear-cut diagnosis. Physical examination was negative except that the patient could not open his mouth more than 8 mm. on the left and approximately 1.4 cm on the right. When the mouth was opened, there was definite deviation of the mandible.