Masticatory muscle tendon-aponeurosis hyperplasia is a new disease entity characterized by limited mouth opening due to contracture of the masticatory muscles, resulting from hyperplasia of tendons and aponeuroses. In the case of masseter muscle type, the face displays a square mandible configuration. Pharmacotherapy, occlusal splints and physical therapy are ineffective. This study evaluated the long-term results of aponeurectomy of the masseter muscle with coronoidectomy to release the temporal muscle tendon. The subjects were 10 patients who underwent surgery between 2000 and 2005. Mean maximum mouth opening before surgery was 21.8mm (range 17-29 mm). All patients received bilateral aponeurectomy of the masseter muscle and coronoidectomy. Three patients additionally underwent bilateral anglectomy for esthetic reasons. After discharge, one patient did not return to the hospital. Data from the other nine patients were analyzed. The mean duration of follow-up was 4 years. At final follow-up, the maximum mouth opening was >44 mm in four patients, 40-44 mm in three patients, and 35-39 mm in two patients. Overall satisfaction was excellent or good in all patients.