Background. This study was performed to ecludate the etiology. effectiveness of diagnostic and therapeutic modaluties, and outcomes in Patients with acute lower gastrointestinal bleeding. Methods. A retrospertive review of the medical records of 1,112 consercultive patients admitted to the surgical service of a single, urban emergency hospital With lower gostrointestimal bleeding from 1988 to 2006. Two groups were compared: 1988-1997 and 1998-2006. Results. All patients undercent colonoscopy, 33.2% within 24 h of admission. Hematochezia was the most frequent presentation (55.5%), followed by maroon stool (16.7%;) and melena (11.0%). Most patients, 690 (62.1%) also had upper endoscopy. Sixty-six patients subsequently had barum enemas Eleven of 27 nuclide scans were positive. Arteriography was performed on. 22 patients, with 11 positive results and 2 therapeutic. No statistical difference was found in procedures performed in our 2 lime periods. Diverticulosis (33.5%), hemorrhoids (22.5%), and carricinoma (12.7%) were the most common etiologies with the diagnosis (of diverticulosis more common in the 1998-2006 time period. The small bowel was the source in 14 total Patients. Spontaneous cessation the bleeding occurred in 863 (77.6% patients.. Endscopic control increased from 1% in 1997-1998 to 4.4% in 1998-2006 (P < 05) with a corresponding decrease in the need for operative control from 22.6% to 16.6% in this same time period P < .05), Furthermore, among elective operations, there was a decrease in right hemicolectomes from 31.6% of total elective ruses to 13.9% (P <.05). Emergent operations were needed in 3.4% and 4.8%. of patients. The readmission rate did not change over time and was 5.2% overall With >50% because of diverticular bleeding. Conclusion. It this urban setting diverticulosis, hemorrhoids, and caramoma were the most common causes of severe acute lower gastromtestimal bleeding (LGIB) with diverticular bleed causing the highest recurrence. Colonsocopy allows for diagnosis in most. patients with. severe acute LGIB requiring hospitalization. Furthermore, it is now being used more effectively for hemostasis resulting in less operative intervention to conlrol bleeding. (Surgery 2009;146-600-7.)