Purpose: Myositis ossificans traumatica describes non-neoplastic heterotopic bone formation in extra-skeletal soft tissues following trauma. When the muscles of mastication are involved, the most reported symptoms are trismus, swelling, and pain. We report the first published case of myositis ossificans involving masticatory muscles following elective orthognathic surgery. Methodology: Myositis ossificans developed in a young patient following an uncomplicated bilateral sagittal split mandibular osteotomy procedure. The patient underwent bilateral coronoidectomy, then commenced non-steroidal anti-inflammatory medical management and physical therapy. Results: Treatment of myositis ossificans of the masticatory muscles is controversial. There is no consensus in the literature with regards to the need for surgical intervention, surgical timing, recurrence rates and the role of non-operative therapies. In this case, despite initial relapse following bilateral coronoidectomy and radiographic evidence of further heterotopic bone formation, sustained increases in mouth opening were achieved with aggressive physical therapy. Conclusion: Myositis ossificans traumatica of the masticatory muscles is rare. In this case, bilateral sagittal split osteotomy was the likely triggering event. While a range of treatments have been described in the literature, there is no strong evidence to support their use. In our experience, aggressive physical therapy may be an effective treatment option.