Acute radiation enteritis is almost inevitable in the curative treatment of malignant tumors of the abdomen and pelvic area. It is frequently a self-limiting disorder of intestinal function associated with reversible mucosal changes of the intestine. The prevalence of chronic radiation enteritis has been underestimated in most surgical series and the majority of patients with symptoms probably do not seek medical advice until a serious complication occurs. Although associated with specific histologic features, the mechanism of chronic radiation injury is poorly understood. The prevalence, pathogenesis, diagnosis and approaches to the treatment and prevention of acute and chronic radiation enteritis are discussed herein. Recent investigative techniques should lead to a better understanding of the physiopathologic characteristics of radiation enteritis and, thereby, provide a more rational basis for treatment which, at the present time, is unsatisfactory. Attempts to reduce the prevalence of radiation enteritis should be directed toward careful patient selection for radiation treatment of the pelvis and to minimize injury to the small intestine, by reducing the volume of small intestine in the radiation area and providing more individualized dosimetry.