The paper describes Kearns-Sayre's syndrome, a rare hereditary neuromu
scular disease, in a patient aged 17 years. The clinical picture of th
e disease had a classical triade: external ophthalmoplegia, pigmentary
retinopathy, and cardiac conduction disturbances. This triade was sup
plemented with other polymorphous symptoms characteristic of the syndr
ome, such as moderate myopathic syndrome, hemeralopia, physical infant
ilism, hypogonadism, pyramidal syndrome. Bifascular block in the His-P
urkinje system was accompanied by mitral prolapse. The problems of ear
ly diagnosis of the syndrome and choice of adequate therapeutical meth
ods are discussed.