Inclusion Criteria:  Osteoradionecrosis in the head and neck area (Stage 1-2b according to the classification by Schwartz and Kagan) Previous radiation with or without chemotherapy of a histologically verified primary tumor in the head and neck area. Patient free of tumor. Autonomous patient. Age ≥18 years old. WHO performance status 0-3. Ability to understand Swedish speech and writing. Received oral and written information about the study and given consent to participate in writing.  Exclusion Criteria:  Contraindications against HBO. Participation in other ongoing study on osteoradionecrosis. Pregnancy or planned pregnancy. Woman in fertile age without effective contraceptive method. Alcohol or drug abuse. WHO performance status 4. Suspicion of recurrent tumor. Mental health disorder or other condition which makes the patient unable to follow study protocol. Not able to give informed concent. Previous HBO.