Nesidioblastosis is an anatomopathological situation defined as the transformation or the exocrine ductal epithelium into endocrine tissue which can be hormonally active or inactive. In this study we present two cases which to our knowledge fulfil criteria for nesidioblastosis. Both patients were male (73 and 45 years, respectively) who were admitted to our department because they presented hypoglycemia. Blood examination revealed the existence of an hyperinsulinism although axial computerized tomography, pancreatic echocardiography and selective angiography of the celiac arterial trunk failed to demonstrate the presence of the tumor in either of the two cases. Due to the persistence of the clinical picture in the first case and to the intolerance to the diazoxide in the second patient, a subtotal pancreatectomy was performed in both cases. The surgical procedure involved removal of the 80% and 75% of the head and body respectively. Both patients are presently free of symptoms although the first patient in under diazoxide therapy due to persistent hypoglycemia (more spaced crisis).