The early detection of allograft rejection remains elusive after solitary pancreas transplantation (PTX). We have previously described a modified technique of cystoscopic transduodenal PTX biopsy using the Biopty gun under ultrasound guidance. During the last 2 years, we performed 24 solitary PTXs with prospective protocol biopsy monitoring as well as biopsies performed whenever clinically indicated. The study group included 17 pancreas transplants alone, 6 sequential pancreas after kidney transplants, and 1 sequential pancreas after liver transplant. Five patients received pancreas retransplants. A total of 92 cystoscopically directed core PTX biopsies were performed, including 50 protocol biopsies (mean 2.1 per patient). Protocol biopsies were performed at 1 month (19), 2 months (3), 3 months (20), 6 months (7), and 12 months (1) after PTX. Adequate PTX tissue for histopathologic examination was obtained in 49 cases (98%). Biopsy findings included no rejection (34), mild rejection (13), pancreatitis (1), and cytomegalovirus infection (1). Overall, 15 of the 49 evaluable biopsies (31%) had significant histopathologic findings. All but 1 of the cases of mild rejection were treated with bolus steroids. Eight of these patients subsequently developed recurrent biopsy-proven rejection within 2 months; 5 grafts were subsequently lost to rejection between 3 and 13 months after PTX. Three biopsy complications occurred: 1 hematoma, 1 pancreatitis, and 1 ileus. Patient survival is 96% and PTX graft survival (complete insulin independence) is 75% after a mean follow-up of 15 months. In the remaining 42 clinically indicated biopsies, 3 were insufficient, 8 showed no rejection, and 31 (79%) had rejection. In half of these cases, the rejection was graded as moderate to severe. In conclusion, prospective monitoring with protocol PTX biopsies may result in the earlier detection of allograft rejection and have a direct effect on improving results after solitary PTX.