Endogenous hyperinsulinism is an abnormal clinical condition that involves excessive insulin secretion, related in 55% of cases to insulinoma. Other causes are possible such as islet cell hyperplasia, nesidioblastosis or antibodies to insulin or to the insulin receptor. Differentiation between these diseases may be difficult despite the use of several morphological examinations. We report six patients operated on for endogenous hyperinsulinism from 1^st January 2000 to 31^st December 2015. Endogenous hyperinsulinism was caused by insulinoma in three cases, endocrine cells hyperplasia in two cases and no pathological lesions were found in the last case. All patients typically presented with adrenergic and neuroglycopenic symptoms with a low blood glucose level concomitant with high insulin and C-peptide levels. Computed tomography showed insulinoma in one case out of two. MRI was carried out four times and succeeded to locate the lesion in the two cases of insulinoma. Endoscopic ultrasound showed one insulinoma and provided false positive findings three times out of four. Intra operative ultrasound succeeded to localize the insulinoma in two cases but was false positive in two cases. Procedures were one duodenopancreatectomy, two left splenopancreatectomy and two enucleations. For the sixth case, no lesion was radiologically objectified. Hence, a left blind pancreatectomy was practised but the pathological examination showed normal pancreatic tissue. Our work showed that even if morphological examinations are suggestive of insulinoma, other causes of endogenous hyperinsulinism must be considered and therefore invasive explorations should be carried out.