Kearns-Sayre syndrome (KSS) is a mitochondrial disorder. There is a large-scale mitochondrial DNA (mtDNA) deletion in most of the cases. In this article, a case of KSS who has progressive external ophthalmoplegia (PEO), retinitis pigmentosa (RP), complete heart block, encephalopathy attacks, type-l diabetes mellitus, ragged-red fiber (RRF) and lactic acidosis is presented and discussed in light of the literature available on this subjects. Diagnosis is confirmed by determination of mtDNA deletion.