Organic or non diabetic hypoglycemia (NDH) is a rare disease when it is confirmed, but is often confounded with low blood glucose concentration (between 3 and 4 mmol/I), which is much more frequent. NDH's definition requires the Whipple triad (plasma glucose level <2.8 mmol/l, symptoms of neuroglycopenia and their relief with administration of sugar). The diagnostic approach needs to differentiate the healthy from the sick patient, who's hypoglycemia causes are multiple and frequent, such as: toxic (medicament, OH), organ deficiency, denutrition and sepsis. When hypoglycemia is suspected, without evident causes in healthy persons, it should be investigated by a 72 h fast test, in order to guide the diagnosis. After confirmation of an endogen hyperinsulinism only, sophisticated imaging should be done to localize the tumor and/or to exclude alternatives diagnosis.