A 51-year-old male visited our hospital for investigation of abdominal pain. Barium enema revealed luminal protruding mass at descending colon, but relatively intact colonic mucosal surface and several orifices with whitish exudates observed during colonoscopic examination, these findings suggested colonic diverticular disease with abscess. Also, specimen from ultrasound guided needle biopsy demonstrated chronic inflammation. Antibiotics applied, but mass lesion showed no improvement. The patient underwent operation two month later, the histologic exam demonstrated mucinous carcinoma. (Intestinal Research 2006;4:106-109)