Diagnostic procedures for secreting endocrine pancreatic tumors comprise biochemical tests, CT scans, conventional abdominal sonography, angiography and occasionally MR imaging and isotope scans. Due to their small size, insulinomas and gastrinomas, the most common of these tumors, elude these diagnostic procedures. Preoperative sonography and CT scans were negative in over 60%, angiograms in 35% of the patients. The example of a patient with insulinoma demonstrates that in the future endosonography will offer itself as an accurate method with little risk.