Forty patients with chronic osteomyelitis were treated with hyperbaric oxygen as an adjunct to surgical therapy and antibiotics and followed for an average of 2 years with a recurrence rate of 15%. The mechanism of action of hyperbaric oxygen in osteomyelitis is probably an indirect one of improving local vascularity and potentiating phagocytosis. Many of these patients represent a refractory group with poor prognosis due to the etiology of the infection, site of involvement, and duration of infection prior to treatment. The recurrence rate following this mode of treatment seems to be primarily related to inadequate surgical management. There was no definite correlation between the site of the infection of pathologic organism and recurrence. Although this is a preliminary report, the results are encouraging. Hyperbaric oxygen may be indicated as an adjunct to good surgical and medical management, particularly in patients with refractory chronic osteomyelitis and in whom ablative surgery is under consideration as the only other means of controlling the infection.