Background: The treatment of pelvic malignancies (uterine, cervix, rectum, etc) often include radiation. Radiation-induced late side effects (longer than 3 months) are developed in 5–10% of those patients. We wanted to investigate the efficacy of hyperbaric oxygen therapy (HBOT) in the management of those patients. Methods: Thirteen women were evaluated. The primary cancer sources were: cervix (7), vagina (2), uterus (2), rectum (1) and bladder (1). All patients were treated with a full pelvic dose of radiotherapy. Eight patients also underwent post-radiation surgery (4 post-hysterectomy, 1 post-colectomy, 1 post-vaginectomy, 1 post-cystectomy and 1 post-exanteration). Eleven patients suffered from pelvic pain, 7 from chronic cystitis (including 2 with vesico-vaginal fistulas), 7 had chronic proctitis (including 2 with recto-vaginal fistulas), 3 had long-standing vaginal ulcers, and one presented with a long-standing open skin wound following surgery. All patients underwent imaging studies and biopsies to rule out active malignant disease, and all received HBOT 100% oxygen, at 2 absolute atmospheres, for 90 minutes (2ATA 90 min). Results: The mean patient age was 61 years (range 32–88). The mean time between completion of radiation therapy and onset of symptoms was 32 months (range 4–60). The patients received an average of 27 HBOTs (range 16–40). Twelve patients reported improvement in pelvic pain, bladder and bowel symptoms and decrease in vaginal discharge. One patient developed lung metastasis and another developed pelvic recurrence. No patient reported side effects associated with HBOT. Conclusion: HBOT appears to be safe and effective in the management of pelvic radiation-induced late side effects, such as soft tissue necrosis (skin and vagina), cystitis, proctitis and fistulas.