Diverticulosis and angiodysplasia are the most common causes of massive lower gastrointestinal hemorrhage. Lower gastrointestinal hemorrhage frequently resolves without determination of a definitive source. An uncommon cause of lower gastrointestinal tract hemorrhage is the small intestinal submucosal aneurysm. This poorly described entity, more commonly recognized as Dieulafoy's disease in the gastric mucosa, has been documented only rarely in the jejunum. We describe a case report of a 27-year-old man with a massive lower gastrointestinal hemorrhage. Diagnostic evaluation failed to identify the source on initial admission. The patient re-presented to the emergency room with recurrent bleeding, anemia, and hypotension. During a period of active bleeding, a number of diagnostic studies ultimately revealed the source to be the proximal jejunum. Inspection of the resected specimen identified a submucosal aneurysm on the mesenteric border. Histologic evaluation identified the pathologic entity as a cirsoid aneurysm.