Sulphonylurea ingestion is life-threatening in toddlers due to its strong and prolonged hypoglycemic effect, and is on the toddlers' "one pill can kill" list. Its administration to children may not be accidental. We discuss a case of non-accidental sulphonylurea ingestion by an 18-month-old girl, and the clinical reasoning process leading to identification of the causative agent for the patient's symptoms. A previously healthy 18 month-old girl presented to the Emergency Department with altered mental status and severe hypoglycaemia, which required intravenous hypertonic dextrose solutions to maintain euglycemia. A family history of type II diabetes prompted a search for sulphonylureas in the child's serum, which was positive. Further investigation led to the conclusion that the child's poisoning was the result of the mother's Munchausen-by-proxy syndrome. Sulphonylurea intoxication should be considered in previously healthy children presenting with hypoglycaemia. More than 20% of sulphonylurea poisonings reported in the literature correspond to Munchausen-by-proxy syndrome or homicide attempts. Initial management consists of rapid glucose infusion, but boluses should be avoided whenever possible to prevent rebound hyperinsulinism and worsening hypoglycemia. We stress the need to consider potential child abuse or neglect in a hypoglycaemic patient with sulphonylurea-using caregivers.