A 20-year-old man with the characteristic findings of infantile onset Kearns syndrome is described. Morphological and biochemical investigations proved a mitochondrial disease which we believe to be the cause of the symptoms in various organs. We assume an autosomal-dominant inheritance, the marker sign of which is blepharoptosis in several family members. Characteristic clinical, morphological and biochemical findings, combined with an autosomal-dominant inheritance with very variable expression, mark the Kearns syndrome as an individual disease, not as a symptom complex (syndrome). Kearns disease can be divided into three forms – an infantile form (‘Kearns-Sayre syndrome’) with early onset, rapid progression, multisystemic involvement and a severe course; and a juvenile and an adult form with onset in the second, respectively third (or later) decades with a generally slower and more benign course and less widespread expression in various organ systems. Furthermore, the occurrence of a curious orthoptic abnormality is described, indicating one of the possible ways to avoid diplopia in chronic progressive external ophthalmoplegia: the coexistence of normal and gliding abnormal retinal correspondence.