This article reviews the clinical behavior, the histologic conditions, and the treatment of a benign osteoblastoma associated with an aneurysmal bone cyst of the mandibular condyle and ramus. A 14-year-old boy, otherwise healthy, was referred for pain and enlargement in his right temporomandibular joint-cheek region. The swelling was firm and tender, a slight facial asymmetry was present, and the mouth-opening capacity was reduced. During a 6-weeks period from the primary examination to surgery the lesion expanded extensively, anesthesia appeared in the right inferior alveolar nerve and a lateral open bite developed on the affected side. Computed tomography displayed a total destruction of the right mandibular condyle and ramus to the level of the mandibular foramen. The lesion was radiolucent without distinct borders to adjacent bone. Surgery revealed a bluish, well-vascularized predominantly cystic tumor. The lesion included the temporomandibular joint disk but without overgrowth to the temporal component. After resection of the lesion, the condyle and the mandibular ramus was reconstructed with the use of an autogenous costochondral graft. The postoperative healing was uncomplicated. At follow-up 2 years after surgery the boy was free of recurrence with normal motor and sensory nerve function.