Hypokalemic periodic paralysis is a rare disorder characterized by reversible attacks of muscle weakness accompanied by episodic hypokalemia. The most common causes of hypokalemic periodic paralysis (HPP) are familial periodic paralysis, thyrotoxic periodic paralysis (TPP) and sporadic periodic paralysis, respectively. There are generally some precipitating factors such as stress, vigorous exercise and high carbohydrate food consumption which all ease the occurrence of attacks. The duration of attacks range from 2-36 hours and can be shortened by K+ supplementation in appropriate situations. 28 years old male, admitted to our clinic with severe weakness at his legs and arms, on laboratory examination severe hypocalemia due to overt thyrotoksicosis detected. After antithyroid drug therapy his symptoms and hypocalemia resolved. After three months of therapy he underwent total thyroidectomy because of incompliance to medical therapy. Rapid recognition and management of the disorder were the key factors to avoid fatal complications.