From May 1988 through May 1991, 14 patients with radiation-induced hemorrhagic cystitis confirmed by cystoscopy and biopsy, who had failed all other attempts at management and who had no evidence of infection or recurrent malignancy, were treated with hyperbaric oxygen therapy. During followup ranging from 10 to 42 months 8 patients (57%) had complete resolution of symptoms and 2 (14%) had marked improvement, for a total of 10 patients (71%) with a positive outcome. Of 4 patients (29%) with a poor outcome 3 had limited improvement and were later diagnosed as having recurrent malignancy that was not present on biopsy before hyperbaric treatment. One patient was withdrawn from hyperbaric treatment due to illness. The average cost per patient was $10,000 to $15,000, comparing favorably to the cost of multiple conservative treatments to control symptoms. Hyperbaric oxygen therapy for radiation-induced hemorrhagic cystitis appears to be an efficacious treatment modality for patients who have failed other forms of management.