Hypokalemic periodic paralysis(HypoPP) is characterized by an abrupt onset of flaccid paralysis with a clear mentality, but muscles of speech and swallowing are usually spared. We report on three patients who suffered attacks of acute paralysis. After exclusion of central nervous system involvement, the patients showing hypokalemia was diagnosed as hypokalemic periodic paralysis, which was completely reversible on parenteral potassium substitution.