Pancreas transplantation is an established treatment for selected type I insulin-dependent diabetes mellitus (DM). Increasingly, enteric drainage of exocrine secretions has been performed in preference to bladder drainage. We present two cases of massive gastrointestinal hemorrhage (GIH) related to arterial-graft duodenal fistulas, a rare cause of massive bleeding. Case 1 DM is a 49-year-old male who underwent simultaneous kidney pancreas transplantation (SPK) for DM and end-stage renal disease (ESRD). He developed a transplant duodenal stump leak that resolved with drainage. He presented with massive hemorrhage at 2 months. Angiography revealed a fistula between the graft-recipient arterial anastomosis and the stump leak. This was managed by transplant pancreatectomy. Case 2 SB is a 37-year-old male who underwent pancreas-after-kidney transplantation (PAK) for type I DM. At 6 months, the pancreas graft failed due to chronic rejection. He presented 9 months later with massive hemorrhage. Upper and lower endoscopy were inconclusive. Angiography revealed a fistula between the transplant arterial graft and the transplant duodenum. This was initially managed by coil embolization and definitively by transplant pancreatectomy. Patients with functional or nonfunctional pancreas transplants presenting with massive GIH not readily localized by endoscopy should undergo angiography to exclude this unusual etiology.