The significant morbidity and mortality associated with pancreatic surgery for isletcell tumors indicate the need for accurate, reliable identification and preoperative localization of insulin-producing islet-cell tumors. The results of this study indicate that angiographic examination of the pancreas can detect such tumors with a degree of accuracy greater than 90 per cent, if attention is paid to the technical quality of the examination. This attention is as important for the accurate diagnosis as are the size, location, and vascularity of the tumor. Vascularity of the tumor as assessed histologically may not have as important a role in the diagnosis as previously suggested.Supplementary techniques such as stereoscopy, subtraction, magnification, and selective injections are also important. We were able to demonstrate 6 of 12 occult insulin-producing islet-cell tumors within the pancreas preoperatively by means of such techniques, which otherwise might have resulted in a partial pancreatectomy without i...