Diagnostic strategies for lower gastrointestinal bleeding include nuclear scintigraphy, mesenteric angiography and endoscopic evaluation of the lower gastrointestinal tract. Each method has inherent advantages and disadvantages. Nuclear scintigraphy is simple and noninvasive, but high rates of false localization have led most clinicians to insist on confirmation of the bleeding site by another method before considering surgical intervention. Angiography is very specific, but is invasive and not as sensitive as nuclear scintigraphy. Colonoscopy is sensitive and specific, and can offer therapeutic value but can be technically challenging in the face of acute lower gastrointestinal hemorrhage. These strategies and the evidence behind them are discussed.