The Kearns-Sayre syndrome is a neuromyopathic disorder associated with mitochondrial abnormalities and characterized by the triad of chronic external ophthalmoplegia, atypical pigmentary retinopathy, and progressive conduction system disorders. Ragged red muscle fibers that seem to contain an excess of altered mitochondria are observed. The disease affects both sexes alike, during the first or the second decade of life. The following manifestations are observed: central bilateral sensorineural deafness, pyramidal signs, ataxia, asymmetrical ptosis, external ophthalmoplegia, and progressive muscular weakness secondary to myopathy associated with a significant increase of proteins of cephalorachidian liquid. A variety of endocrinopathies may occur.