Gastrointestinal bleeding appears to be uncommon in patients with AIDS. The incidence, etiology and characteristics of upper GI bleeding have been described in the literature. However, the data regarding lower gastrointestinal bleeding (LGIB) are limited. Aim: To study the incidence, etiology and other characteristics of LGIB in patients with AIDS and compare with a cohort of non-HIV-infected patients with LGIB. Methods: All AIDS patients with LGIB seen by gastroenterology consult service at Grady Memorial Hospital 8/90 to 8/96 were considered eligible. Non-HIV-infected patients with LGIB admitted to the hospital during 8/94 to 8/96 were identified as the control group. LGIB was defined as passage of bright red or maroon-colored stool with a source of bleeding distal to the ligament of Trietz with a subnormal hematocrit or a drop in hematocrit more than 5% from the base line. Results: Of the 691 AIDS patients seen during the study period, 18 patients had LGIB (2.5%). The control group comprised 48 patients. AIDS (18) Control (48) P-value Most common cause CMV (39%) Divertculi (62%) - Recurrence 4(22%) 14(29%) 0.7 Medical treatment 7 0 0.00004 Surgery 0 15 0.0006 Death in hospital 5 1 0.004 Death within 6 months 30 0 0.02 Causes of bleeding in AIDS: CMV colon disease (7), Idiopathic colon ulcers (5), hemorrhoids (3), anal fissure (1), small bowel Kaposi's (1). Conclusions: 1) LGIB seems to be infrequent in patients with AIDS and its etiology is entirely different in AIDS, with CMV colon disease being the most common cause. 2) Compared to non-HIV-infected patients with LGIB, AIDS patients have more medically treatable causes; nevertheless their survival is poor.