A 2-year-old female Burmese cat was referred to the University Hospital of Companion Animals of Utrecht University because of periodic muscle weakness and cervical ventroflexion. Laboratory examinations revealed hypokalemia. The combination of breed, clinical signs and hypokalemia warranted the diagnosis of 'periodic hypokalemic myopathy', a homozygote recessive hereditary disease in Burmese cats. Potassium supplementation resulted in complete disappearance of the signs. Possible causes of hypokalemia in the cat are discussed.