Stress hyperglycemia in children is considered a benign condition that usually does not mandate further investigation. In some clinical settings it might be the first sign of diabetes mellitus (DM). Two unrelated boys, one aged 2 years 7 months and the other aged 5 days, were evaluated in the emergency department for a febrile infection and found to have elevated blood glucose levels (238 and 150 mg/dL [preprandial], respectively). In both cases the elevated hemoglobin A1c levels (6.5% and 6.6%, respectively) combined with a history of gestational DM in the mother and positive family history for DM suggested maturity-onset diabetes of the young. Genetic analysis revealed 2 known heterozygote mutations in the glucokinase gene: c.697T→C p.C233R in the first case and c.616A→C p.T206P in the second case. Our findings suggest that stress hyperglycemia during early childhood in association with a positive family history of DM might be a sign of monogenic diabetes.