We report a case of fatal hyponatremic encephalopathy in a child who was forced to exercise as a form of punishment. A 9-year-old girl with attention-deficit/hyperactivity disorder was forced to run repeated 50-ft sprints to the point of exhaustion by her grandmother as punishment for taking candy from a classmate. After more than 3 hours of forced running, the child collapsed, began to vomit, and had repeated clonic seizures. Upon presentation to the emergency department, she was nonresponsive with a Glasgow Coma Scale score of 11 and had noncardiogenic pulmonary edema with serum sodium of 117 mEq/L. She was treated with antiepilectic medications and transferred to a university children’s hospital where she later died. On postmortem examination, she was found to have massive cerebral edema with transtentorial herniation and pulmonary edema. Her clinical presentation closely resembled exercise-associated hyponatremic encephalopathy seen in adult endurance athletes. This appears to be the first report of fatal exercise-associated hyponatremia in a child.