On the bases of personal experience and the series of 148 cases from an international inquiry and a review of the literature, the relation between insular hyperplasia and hypoglycemia was examined. The fundamental points in this investigation included: age, diagnostic investigations, histological findings and postoperative results. The data on the patients with insular hyperplasia indicates that 83% were of adult age. Insular hyperplasia was the only abnormal factor determined to be present. Through treatment a high percentage of cases (71%) was cured. From a practical surgical point of view, differentiation between occult insulomas and insular hyperplasia is not critical. Consequently, good results can be achieved in botlh diseases by practicing a progressive blind resection guided by examination of the operated specimen and by intra-operative blood sugar levels.