Osteoradionecrosis (ORN) is a known complication to radiation therapy for head and neck cancer with a prevalence of 5–7% among radiated patients. Treatment might include dental surgery and reconstruction of the jawbone as well as hyperbaric oxygen treatment (HBOT). HBOT takes place in a closed compartment where patients are breathing 100% oxygen under pressure for 90 minutes once a day every weekday for 6 weeks. In Denmark, HBOT is available at two facilities with very different organizational set-ups.