Hemorrhagic cystitis after radiotherapy is clinically important because it is relentlessly progressive, and treatment options are suboptimal.(1) The treatment of this entity depends on its extent and severity.(2,3) We present the sonographic findings in a case of hemorrhagic cystitis secondary to pelvic irradiation before, during, and after hyperbaric oxygen (HBO) therapy. The pathophysiologic characteristics of hemorrhagic cystitis and the mechanism of HBO therapy are also discussed.