Background: Although hematochezia is well recognized to occur in patients with upper GI hemorrhage (UGIH), its prevalence, clinical presentation, causes, and outcome in these patients are not well defined. Methods: Consecutive patients evaluated for UGIH by the gastroenterology service at a large inner city hospital from August 1, 1990, through September 31, 1994, were prospectively identified. Vital signs and stool color were recorded on admission to the emergency department. Endoscopy was performed in all patients, usually within 48 h of admission. The cause of bleeding was determined by endoscopy, surgery, or autopsy. Results: Over the 50-month study period, 727 patients with UGIH meeting the inclusion criteria were evaluated, with 104 (14%) presenting with hematochezia (18 with bright red blood and 86 with maroon blood). The most common causes of bleeding were duodenal ulcer (44%) and gastric ulcer (20%). In comparison with patients with melena (N = 441), patients with hematochezia were older (55 vs 50 yr, p < 0.01) and more likely to present with duodenal ulcer bleeding (43 vs 25%, p < 0.01); no differences in vital signs, including prevalence of shock, or admission Hb concentration were found. However, transfusion requirements (5.4 vs 4.0 units, p = 0.01), need for surgery (11.7 vs 5.7%, p = 0.03), and mortality (13.6 vs 7.5%, p = 0.05) were significantly higher in patients with hematochezia than in those with melena, suggesting more severe bleeding and a worse outcome. Conclusions: Hematochezia is common in patients with UGIH, and the presenting features are similar to those of patients with melena. Duodenal ulcer is the most common cause of bleeding associated with hematochezia. Patients with UGIH and hematochezia seem to have a worse prognosis.