A 52-year old man came to the emergency department after ten days of steadily worsening crampy pain in the left flank and iliac fossa. His medical history was unremarkable. He had stopped smoking ten years previously (15 pack-years). The temperature was 38.8 C. Physical examination of the lower abdomen elicited some guarding, but the abdomen was otherwise supple with no palpable mass. The leucocyte count was normal. He was admitted to hospital. An abdominal CT scan showed features compatible with colitis, probably ischemic, extending from the splenic angle to the rectum. The bowel wall was thickened with “infiltration” of the surrounding fat. A 3 cm left renal mass was also noted. Although colonoscopy showed colitis of irregular distribution, perhaps infectious, a biopsy specimen revealed normal colonic mucosa. The patient was discharged with a prescription for an antibiotic. Four days later he returned to the emergency department with pain similar to that at his first admission. He was admitted to hospital. A CT scan was performed which showed a markedly thickened mesentery and a thickened, non-enhancing left colonic wall. The inferior mesenteric artery was irregular, tortuous and stenosed; there was no intravascular thrombosis. Based on these findings, vasculitis was initially considered. Colonoscopy showed marked edema of the mucosa. A biopsy specimen showed ischemic changes. Three weeks later a diagnostic laparoscopy was performed which found ascites and multiple whitish epiploic appendices, one of which was biopsied with a subsequent microscopic diagnosis of fat necrosis. A loop colostomy was performed. Six weeks later symptoms of large bowel obstruction developed; a left hemicolectomy with transverse colostomy was therefore performed. During the same intervention a left partial nephrectomy was carried out. The rectal stump was left open with a drain. The renal mass showed microscopic features characteristic of an oncocytoma. Macroscopic examination of the recto-sigmoid resection specimen showed diffuse hemorrhagic necrosis of the mucosa and marked bowel wall thickening with massive mesenteric necrosis. Necrotic fat encased the whole length of the resected bowel. Microscopic examination confirmed marked ischemia and ulceration of the colonic mucosa. The mesentery showed findings typical of fat necrosis. Numerous arteries and arterioles within the necrotic fat were obstructed to varying degrees, often completely, by fibrosis of the intima; the media of these vessels was normal. Atheromata, thrombosis, and inflammation were absent. The changes were considered diagnostic of fibromuscular dysplasia, intimal-type. The postoperative course was uneventful and the patient was discharged home. Ten months later, he is asymptomatic and he is due to have his colostomy reversed.