Kearns-Sayre syndrome (KSS) is a multisystem mitochondrial disorder characterized by the invariant triad: onset before 20, progressive external ophthalmoplegia and pigmentary retinal degeneration, plus at least one of the following: complete heart block, cerebellar dysfunction and CSF protein >100 mg/dl. Autopsies from patients with KSS revealed widespread tissue distribution of mitochondrial (mt) DNA deletions. These deletions result in significantly lower activities of the enzymes of the respiratory chain. KSS has been associated with a variety of endocrine and metabolic disorders in <10% of patients, while renal tubular involvement is extremely rare. We present an 18-year-old girl with KSS who developed hypoparathyroidism and renal tubular dysfunction with inappropriate mangesiuria and kaliuria. We further discuss the renal tubular damage in KSS emphasizing its pathophysiology and clinical phenotype, and review the possible mechanisms of hypoparathyroidism in KSS.