We report a case of adenocarcinoma that developed in an ileal conduit 18 years after cystectomy for transitional cell carcinoma of the bladder. The only presenting sign was gross hematuria. Retrograde ileal loopography and endoscopy of the ileal loop were useful in the diagnosis. To our knowledge adenocarcinoma arising in an ileal conduit after a radical procedure for transitional cell carcinoma of the bladder has not been reported previously. The literature regarding malignancies that arise in portions of intestinal segments used as conduits is reviewed and carcinogenesis is discussed.