Background: CMV colitis is a common opportunistic infection in patients with AIDS. However, the endoscopic appearance and patterns of disease have not been well characterized. Methods : Human immunodeficiency virus (HIV)-infected patients undergoing sigmoidoscopic or colonoscopic evaluation at two institutions for clinical indications were prospectively identified. CMV was diagnosed histologically based on published criteria and all pathologic specimens were reviewed prospectively by the authors. At the time of endoscopic evaluation, the location, size and appearance of all lesions were documented. Results : 45 patients (38 males; mean age 39±9 years; range, 27-65) were studied. The most common risk group was homosexual contact (78%) with a prior AIDS defining diagnosis seen in 28 patients (621). The median duration of symptoms was 11 weeks with diarrhea (80%) and abdominal pain (38%) being most frequently reported. The colonoscopic appearanee could be characterized into 3 distinct patterns:single or multiple ulcers alone (42%), multiple ulcers associated with colitis (38%), and colitis without ulcer (20%). of the 22 patients undergoing colonoscopy, the disease was pancolonic in 11 and proximal to the sigmoid colon in 3. Ulcers ranged in size from 3 mm to 10 cm. with a pattern typical for Crohn's disease found in 2 patients. Conclusions: 1) . CMV colitis most commonly appears as one or multiple ulcerations often with colitis. 2. The distal colon appears to be the most common location of disease.