Sternal infection and mediastinitis are uncommon but serious complications after cardiothoracic surgery via median sternotomy. They increase postoperative mortality, morbidity and overall cost. Early aggressive debridement and empiric antibiotic use are the primary treatment. The postulated mechanism of ischemia and hypoxia resulting in the development of sternal infection and mediastinitis provides a theoretical basis for the use of hyperbaric oxygen therapy (HBO). A review of case reports and some nonrandomized studies found that they all supported the use of HBO for sternal infection after cardiothoracic surgery. We report a case of sternal wound infection and osteomyelitis after median sternotomy. The patient received wound debridement and antibiotic treatment but without effect. After adjunct hyperbaric oxygen therapy, the sternal infection and mediastinitis improved dramatically and the patient was discharged without co-morbidity. We concluded that HBO therapy may be a variable adjunct treatment for sternal infection and mediastinitis after sternotomy.