Coronoid process hyperplasia is one of a large number of disorders affecting the stomatognathic system and causing mandibular hypomobility. It is characterized by an excessive coronoid process growing to such an extent that it impinges on the posterior portion of the zygomatic bones. Despite the low prevalence of this condition, it should be considered as a possible diagnosis in patients with painless, progressive, and chronic restriction of mouth opening. The diagnosis is based on clinical signs in association with radiographic examinations. Coronoidectomy is the only treatment option for this condition along with early postoperative physical therapy. This article presents the case of a patient with bilateral coronoid process hyperplasia, who was initially diagnosed as having bilateral temporomandibular joint disorders. The patient underwent months of physiotherapy and bite-appliance therapy without any improvement in mouth opening. FinalIy, he was referred to La Timone Hospital for a proper diagnosis and, consequently, effective treatment.