Hyperbaric oxygen (HBO) increases oxygen availability to hypoxic tissues thereby inducing fibroblastic proliferation and capillary formation in bone and soft tissue. From 1981 to 1991 we used a monoplace hyperbaric chamber, and since 1992 a multiplace chamber, for HBO treatments. HBO was given at 2.5-2.8 atm abs for 90-120 min, once per day. We used five to seven preoperative and five to seven postoperative sessions. Altogether, 17 patients with osteoradionecrosis (ORN) of the mandible or maxilla were treated with surgery and HBO. Surgical therapy consisted of decortication of the affected bone that was subsequently covered with a free periosteal transplant from the tibia. The shortest follow-up time is 18 mo. Sixteen patients have remained symptom free after the first treatment period. One case was a failure in the early protocol but was successfully treated using a free microvascular flap. It is concluded that HBO is a promising adjunct to surgery in treating mandibular or maxillary ORN.