The advent of fiberoptic endoscopy, which became widespread in the evaluation of gastrointestinal bleeding throughout the late 1970s and 1980s, has dramatically changed both our understanding of the extent to which vascular malformations account for gastrointestinal blood loss and our ability to treat these lesions at the time of diagnosis. Colonic vascular malformations appear to be the single most common cause of acute or recurrent gastrointestinal bleeding episodes in patients over 60 years of age, being responsible for the bleeding in as many as 35% of such patients. Although less common as a cause of upper gastrointestinal bleeding, these lesions still account for 2% to 5% of bleeding lesions in older patients. Diagnosis is accomplished by endoscopy, and the vascular malformations can then be coagulated via the endoscope using one of a number of thermal systems. The argon laser, the heater probe, and the BICAP system are all effective and safe throughout the gastrointestinal tract, especially in the cecum and right colon, where the majority of sporadic vascular malformations occur. Monopolar cautery and the Nd:YAG laser are equally efficacious, but their greater and less predictable depth of coagulation make them much less safe in the cecum and right colon. There are no apparent advantages in terms of efficacy and safety between laser treatment and the other thermal modalities. The laser has the advantage of being quicker, which is especially important when treating large or multiple lesions. The other modalities have the advantages of portability and low relative cost. Endoscopic therapy with lasers or other thermal devices is nonspecific. The effects are achieved by thermally coagulating the mucosal vascular lesions, allowing the coagulated tissue to slough, and leaving a mucosal ulceration that subsequently heals with re-epithelialization. Endoscopic coagulation has thus been reported effective in the treatment of gastrointestinal mucosal vascular lesions regardless of their etiology or characteristics. It has been effective for sporadic vascular malformations, hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu disease), radiation proctocolitis, the blue rubber-bleb nevus syndrome, and diffuse gastric antral vascular ectasia (the watermelon stomach). As we move through the 1990s and beyond, these endoscopic modalities offer an effective, relatively safe, and clearly less invasive treatment option for the many patients who experience acute, recurrent, or chronic gastrointestinal bleeding from any of these lesions.