53 year-old man who had undergone aortic aneurysm repair 10 months previously, was found to be iron deficient. There was no history of gross bleeding. Barium enema demonstrated an apparent ulcerated neoplasm in the sigmoid colon. At colonoscopy, the lesion appeared to be a smooth, brown, dome-shaped "tumor" surrounded by inflamed, benign-appearing musoca. The lesion was not pulsating; it felt quite firm on touch with a biopsy forceps. A gentle attempt to obtain a biopsy was not successful, and no vigorous attempts to obtain biopsies were made. At surgery, the lesion proved to be the left iliac limb of the aortic Y-graft, which had eroded through the full thickness of the wall of the sigmoid colon.