Generalized weakness of acute onset, apparent muscular pain, and persistent ventroflexion of the neck were observed in 6 cats. These clinical signs were associated with a low serum potassium concentration and high serum creatine kinase activity. Generalized electromyographic abnormalities, together with normal motor nerve conduction velocity determinations, were detected in all cats. Muscle biopsy specimens from 4 of 5 cats were not abnormal on light microscopic examination. Mild necrosis and infrequent macrophages were evident in a muscle biopsy specimen from one cat. Signs of polymyopathy resolved in all cats, and creatine kinase activities returned to the normal range after parenteral and oral administration of potassium. Polymyopathy and hypokalemia recurred in 3 cats in which dietary potassium supplementation was not maintained after initial recovery from hypokalemic polymyopathy.