A case of bilateral coronoid enlargement resulting in restricted opening of the mandible has been presented, and the literature has been reviewed. This case brings the total number of reported cases to 36. As in the majority of the previous cases, this patient was male, and the abnormality was first noticed at the onset of puberty. The radiologic features were diagnostic: the restricted mandibular motion was secondary to coronoid process impingement on the posterior aspect of the zygomatic bones. A large exostosis had appeared on the left humerus at approximately the same time as the onset of the limitation of mouth opening. The patient refused surgery because he did not believe that the abnormality caused any significant functional impairment.