Thyrotoxic hypokalemic periodic paralysis is characterized by attacks of generalized weakness associated to hypokalemia in patients with hyperthyroidism. We report a 25-year-old man with a history of spontaneously relapsing episodes of muscular weakness, who consulted for a rapidly evolving upper and lower limb paresis. Hypokalemia associated to a primary hyperthyroidism was detected. Treatment with antithyroid Drugs and potassium supplementation reverted symptoms and the episodes of acute muscular weakness did not reappear.