Thyrotoxic periodic paralysis is a reversible metabolic disorder that is characterized by acute muscle weakness and hypokalemia. It predominantly affects males of Asian descent. We describe the youngest such patient yet reported, a 13-year-old Asian male with a history of transient attacks of weakness who presented to our emergency department with weakness in his extremities and mild tachycardia. Laboratory test results initially revealed marked hypokalemia and later confirmed associated hyperthyroidism. Correction of the hypokalemia reversed the patient's weakness in the emergency department.