Over the past 25 years and more, very few statistically reliable evaluations dealing with clinicopathologic features of patients with insulinoma and/or hypoglycemic syndrome (HGS), including recently popularized diagnostic modalities, have been published. The aims of this study are threefold: first, to evaluate the clinicopathologic features of patients with insulinoma/HGS from various viewpoints; secondly, to update our knowledge about this subject which has been retained up to date, and thirdly to supply reliable information to investigators working in the specialized field of gut-pancreatic endocrinomas. We collected data from literature on a total of 1085 Japanese patients with insulinoma/HGS and undertook a statistical evaluation. The results are summarized as follows. 1) Association of HGS was recognized in 88.4% of the 1085 patients. 2) Islet B-cell hyperplasia/nesidioblatosis was found in 4.1%; 2.6% in association with insulinoma and 1.6% without it. 3) Patients with small tumors of 20 mm or less comprised 81.1%. 4) The overall rate of metastases was 6.6% (72 patients) and that of malignancy 13.6% (148 patients). 5) Multisecretors immunohistochemically proved were found in 32.4% and multiplicity of tumor growth in 12.6%. 6) The 10-year survival rate after removal of lesions was 90.5% overall; 98.4% in patients with benign lesions and 75.7% in those with malignant tumors. It is expected that the results obtained in the present study will provide extensive and useful information for future investigation.