Radiation is an integral part of therapy for many pelvic cancers, including rectal, prostate, cervical, and uterine cancers, and has been shown to decrease local recurrence and increase patient survival. Radiation injury is a sequela of treatment that manifests different symptoms depending on the organ affected. This review covers disease pathology, risk factors, disease prevention, clinical presentation, medical therapy, endoscopic therapy, and surgical therapy. Tables outline risk factors predisposing patients to the development of radiation injury, investigated prophylactic therapies to prevent radiation injury, reported frequencies of symptoms of chronic radiation proctitis, pharmacologic therapies that have demonstrated clinical benefit in randomized trials, and a scoring system for symptoms and endoscopic and histologic results. A management algorithm details evaluation and treatment of radiation-induced gastrointestinal injury. A microscopic section shows diffuse ulceration and granulation tissue formation. Photographs depict the rectal wall thickened by dense white tissue and severe perianal dermatitis. Endoscopic views of radiation proctitis with ulceration, severe radiation proctitis, mild radiation proctitis, prominent telangiectasia, anal necrosis due to radiation, actively bleeding telangiectasia, and argon plasma coagulation are provided. Other figures include computed tomographic scans of an inflamed rectum and the rectal wall with thin mucosa, and magnetic resonance imaging of the pelvis. This review contains 13 figures, 5 tables, and 89 references.