The effects of fasting on preoperative glycemic levels and the influence of different intravenous solutions on postoperative sugar levels are discussed. Sugar levels were determined in 90 children, randomly placed in three groups, (according to the solution they were administered-A: Ringer-lactate, B: glucose at 5%, C: mixed-2 x 1) at the time they entered the hospital, after fasting previous to the anesthetic induction, and in the immediate postoperative period. In 14.4% of the cases hypoglycemia was found during the anesthetic induction, increasing as the fasting period was prolonged. The postoperative hyperglycemia seen in Group B was important, the other groups showed no significant changes. We recommend that the fasting period be no longer than 12 hours and to immediately start intravenous restitution if this period is extended further. Also, only Ringer's lactate solution or a 2 to 1 mixture is recommended to be used during surgery in order to avoid preoperative hypoglycemia and postoperative hyperglycemia. Glycemia; fasting; perioperative solutions.