Metformin is a widely used biguanide for the treatment of type 2 diabetes mellitus. Metformin-induced lactic acidosis (MALA) is a rare but potentially fatal entity in the pediatric age group, seen mainly in suicide attempts in adolescents. MALA has not yet been reported in younger patients or pediatric patients taking regular therapeutic doses. Here, we report a three-year-old female receiving therapeutic metformin who developed MALA. MALA should be suspected in patients with unexplained lactic acidosis and on regular metformin, especially in the setting of renal impairment or hypoxic events.