A 46-yr-old man, in whom retroperitoneal fibrosis had been found 4 yr previously, presented with abdominal pain, fever, diarrhea, and marked dilation of the transverse colon with superficial ulceration. The megacolon was unresponsive to nasogastric suction, corticosteroids, antibiotics, and total parenteral nutrition. Arteriograms revealed total occlusion of the celiac axis and superior and inferior mesenteric arteries. Laparotomy showed encasement of the retroperitoneal vessels by dense fibrous tissue. A vascular bypass graft was performed, connecting the distal superior mesenteric artery to the right external iliac artery. This led to complete and lasting resolution of gastrointestinal complaints.