Two cases of bilateral coronoid hyperplasia resulting in restricted jaw movement are presented.A 21-year-old man had been aware of limited mouth opening at age 15 and the condition worsened gradually. The maximum mouth opening was 14mm between upper and lower central incisors. Protrusive movement and lateral excursion were also limited.The other patient, a 19-year-old man, had been aware of limited mouth opening at age 16 and the condition worsened gradually. The maximum mouth opening was 20mm between upper and lower central incisors. Protrusive movement lateral excursion were also limited.In both cases, no history of local or systemic infections or trauma could be elicited, and no other family nember was similarly affected.Panoramic radiographs and tomograms of the mandible showed that the bilateral coronoid processes extended above the zygomatic arch, and their anterior margins were situated close to the posterior aspect of the zygomatic bones.Bilateral coronoidectomies were performed via intraoral approach under local anaesthesia. Histologically the specimens were not tumor, but hyperplasia of coronoid processes. PostZ operative jaw exercise was encouraged.In both cases normal jaw function was observed 3 months after surgery.