Kearns-Sayre syndrome (KSS) is a form of mitochondrial myopathy in which specific clinical features, namely progressive external ophthalmoplegia, pigmentary retinal degeneration and onset before age 20 occur. It can also be associated with cardiac conduction defects, neurological and variety of endocrine and metabolic disorders. Recognition of mtDNA deletion as the genetic basis of KSS has confirmed the validity of clinical criteria. The purpose of the report is to describe a 30-year-old woman presenting typical clinical features of KSS. On muscle biopsy ragged red fibres and mitochondrial abnormalities on electron microscopy were seen. In spite of menstrual disturbances she became pregnant and delivered health child. In 30 week of pregnancy the VVI pacemaker was implanted because of syncope most probably related to paroxysmal complete heart block.