Shaw and Baue1 first described the use of iliofemoral bypass through the obturator foramen for patients with sepsis in the groin following arterial reconstructive surgery. This procedure has since been applied to patients who have carcinomatous overgrowth, radiation necrosis, ischemic skin flaps or trauma to the overlying soft tissues in the femoral triangle.2 Guida and Moore2 have recently presented an excellent description of the operative technique. The increasing incidence of narcotic addiction with "main lining" of heroin into the femoral vein has resulted in a growing number of patients with a "mycotic aneurysm" of the groin. Since November 1967, we have encountered five such patients at Detroit General Hospital. The lessons learned in these patients are the subject of this report. Report of Cases Case 1.—A 53-year-old man presented to the emergency room on Jan 3, 1968, with a three-day history of swelling and pain in the