Tumors arising from the pancreatic endocrine (islet) cells represent a heterogeneous group of lesions. Some tumors present with well characterized syndromes, while others appear to be nonfunctioning. Eighteen patients with pancreatic endocrine tumors who received surgical treatment at Kurume University Hospital during a 24-year period were reviewed. There were 10 patients with nonfunctioning tumors including 3 patients with benign tumors, and 8 patients with insulinomas. No patients had multiple endocrine neoplasms. Location of the pancreatic tumor was determined preoperatively in 83.3% of the patients. Immunohistochemical analysis of the resected specimens showed multi immunoreactivity to gut hormones among benign lesions and one malignant lesion, whereas malignant lesions showed no or mono immunoreactivity except in one case. In this series, there were no characteristic immunohistochemical findings in the tumors. Both patients with malignant and benign lesions have good prognoses if the main tumors and metastatic lesions are removed.