Introduction Acute lower gastrointestinal bleeding (ALGIB) is a common event, which consumes considerable human and economic resources. Its incidence is expected to rise in the coming years due to an increasing aging population. Patients and methods Multicentric prospective analysis of patients was carried out with ALGIB in 13 Portuguese hospitals from April 2008 to May 2009, using a protocol designed by the French Association Nationale des Hepato-Gastroenterologues des Hopitaux Generaux. Statistical analysis was carried out with SPSS 16.0. Results In a total of 371 hemorrhagic events in 364 patients (51.4% men, mean age: 72 years), 28.4% patients showed hemodynamic instability and 54.2% were under single/combined medication with antiaggregants/NSAIDs/heparin/anticoagulants; blood transfusion was administered in 34.8% of patients. Sigmoidoscopy was the first endoscopic procedure performed in 61.3% of patients and rectal enema was the first method of bowel preparation in 67.3% of them. Endoscopic hemostasis was performed in 22.2% of all cases with efficacy ranging from 84.6 to 96.2%. Most frequent diagnoses were ischemic colitis (23.7%), diverticulosis (20.8%), and colorectal malignancies (12.4%). Surgery was needed in 8% of patients, and global mortality rate was 2.2%. Risk factors for poor outcome on multivariate analysis were heparin use before bleeding (hazards ratio: 10.6; 95% confidence interval: 0.94-119.48) and in-hospital bleeding (hazards ratio: 5.6; 95% confidence interval: 1.01-19.70). Conclusion ALGIB seems to occur frequently in Portugal with a low mortality rate. Previous heparin use and in-hospital bleeding are associated with worse prognosis. Our management relies on early endoscopic examinations, which are highly available, safe, and accurate. A successful endoscopic therapeutic approach was possible in one fifth of the patients. Eur J Gastroenterol Hepatol 23:317-322 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.