Angiodysplasia (AD) may be the source of bleeding in patients with gastrointestinal hemorrhage, with special occurrence in the elderly population and in patients with chronic renal failure (CRF). Although several techniques have been tested for its diagnosis, the gold standard is not well defined yet. We analyze the usefulness of ^99mTc-labelled red blood cell (^99mTc RBC) scintigraphy in the localization of bleeding from AD lesions in a cohort of 21 patients. Other investigative methods include fibrocolonoscopy examination, angiography, or diagnostic laparotomy. Group A (AD and CRF): 11 patients. Group B (AD without CRF): 10 patients. ^99mTc RBC scintigraphy showed 88.9% sensitivity and specificity in group A, while in group B it had 100% sensitivity and specificity. Arteriography showed 100% sensitivity and specificity. On the contrary, fibrocolonoscopy had a very low sensitivity (30%). Our results suggest that ^99mTc RBC scintigraphy may be the preferred diagnostic tool for AD, especially in patients with CRF, in whom arteriography may accelerate the decline of renal function.