There are few cases published in literature in which the use of intravenous dextrose as treatment for an insulinoma resulted in a metabolic acidosis. This is due perhaps to the usual method of administration, which is usually at low concentrations, for limited periods or low volumes. We present the case of a woman with suspected insulinoma by laboratory findings in which an endogenous hyperinsulinism was observed. During hospitalization, the patient required a progressive increase of the glucose infusion to prevent severe hypoglycemia. Two days before surgery, the patient presented symptoms of malaise and muscle weakness and a metabolic acidosis with hypokalemia became apparent in the blood analysis. This metabolic imbalance was attributed to a long period of treatment with high volume of intravenous dextrose infusion. If large doses of dextrose are required in a patient with an insulinoma, then the possibility of a metabolic imbalance must be considered during the follow-up. When the suspicion of an insulinoma is high, and all the attempts of pre-operative localization fail, patients should be derived early to specialized centers with modern imaging techniques, so that surgery is not delayed, and this rare and threatening complication could be avoided.