Eleven cases of pancreatic islet cell tumors were reviewed to compare diagnostic ability of endoscopic retrograde pancreatography (ERP) with other imaging modalities. ERP localized three out of five tumors studied and showed a suspicious finding in an additional patient. All these tumors were located in the pancreatic head. Thus, the diagnostic ability of ERP was superior in the head portion, where recognition of a tumor is often difficult at the operation, and a more complicated procedure is required for removal. Nonfunctioning islet cell tumors were localized by hypervascularity on angiogram, but retroperitoneal leiomyosarcoma remained to be excluded in one patient. ERP with an indwelling balloon catheter revealed the pancreatic origin of the tumors and precisely determined the line of pancreatic resection by vividly visualizing pancreatic duct obstruction and intact distal branches. We conclude that ERP is helpful to localize functioning islet cell tumors of the pancreas especially in the head portion and plays an important role for planning resection of nonfunctioning islet cell tumors.