• The Kearns-Sayre syndrome (KSS) appears to be a distinctive disorder characterized by progressive external ophthalmoplegia, pigmentary degeneration of the retina, heart block, and elevated CSF protein levels. Recent reports have suggested that abnormalities of muscle mitochondria may also be a consistent finding in KSS. We recently examined a patient with KSS whose skeletal muscle contained abnormal mitochondria. In addition, a computerized tomographic scan of the head showed cerebellar and brain stem atrophy, as well as calcification in the region of the basal ganglia.