Evaluation and management of acute lower gastrointestinal bleeding focus on etiologies originating distally to the ligament of Treitz. Diverticular disease is the most common source, accounting for 40% of cases. Hemorrhoids, angiodysplasia, infectious colitis, and inflammatory bowel disease are other common sources. Initial evaluation should focus on obtaining the patient's history and performing a physical examination, including evaluation of hemodynamic status. Subsequent evaluation should be based on the suspected etiology. Most patients should undergo colonoscopy for diagnostic and therapeutic purposes once they are hemodynamically stable and have completed adequate bowel preparation. Early colonoscopy has not demonstrated improved patient-oriented outcomes. Hemodynamic stabilization using normal saline or balanced crystalloids improves mortality in critically ill patients. For persistently unstable patients or those who cannot tolerate bowel preparation, abdominal computed tomographic angiography should be considered for localization of a bleeding source. Technetium Tc 99m-labeled red blood cell scintigraphy should not be routinely used in the evaluation of lower gastrointestinal bleeding. Surgical intervention should be considered only for patients with uncontrolled severe bleeding or multiple ineffective nonsurgical treatment attempts. Percutaneous catheter embolization should be considered for patients who are poor surgical candidates. Treatment is based on the identified source of bleeding.