In this prospective cohort study, the effects of hyperbaric oxygen treatment (HBOT) were evaluated concerning patient-perceived symptoms of late radiation-induced cystitis and proctitis secondary to radiation therapy for pelvic cancer. Thirty-nine patients, 35 men and 4 women with a mean age of 71 (range, 35-84) years were included after informed consent and institutional ethics approval. They had all been treated with radiation therapy for prostate (n=34), cervix (n=2), or rectal (n=3) cancer using external beam radiation at a dose of 25 to 75 Gy. Patients with hematuria requiring blood transfusion were excluded. The HBOT was delivered with 100% oxygen for 90 minutes at 2.0 to 2.4 atmospheres (ATA). Mean number of treatments was 36 (28-40). Symptoms were prospectively assessed using the Expanded Prostate Index Composite score before, during, and 6 to 12 months after HBOT. The HBOT was successfully conducted, and symptoms were alleviated in 76% for patients with radiation cystitis, 89% for patients with radiation proctitis, and 88% of patients with combined cystitis and proctitis. Symptom reduction was demonstrated by an increased Expanded Prostate Index Composite score in the urinary domain from 50±16 to 66±20 after treatment (P<.001) and in the bowel domain from 48±18 to 68±18 after treatment (P<.001). For 31% of the patients with cystitis and 22% with proctitis, there were only trivial symptoms after HBOT. The improvement was sustained at follow-up in both domains 6 to 12 months after HBOT. No severe side effects were observed related to HBOT, and treatment compliance was high. HBOT can be an effective and safe treatment modality for late radiation therapy-induced soft tissue injuries in the pelvic region. Oscarsson, Arnell, Lodding, Ricksten, Seeman-Lodding, , , , (2013). Hyperbaric oxygen treatment in radiation-induced cystitis and proctitis: a prospective cohort study on patient-perceived quality of recovery. International journal of radiation oncology, biology, physics, 2013 Nov;87(4):670-5. https://www.ncbi.nlm.nih.gov/pubmed/24035333