Mitochondrial cytopathies are metabolic diseases, expressing mutations in nuclear DNA, punctiform mutations or depletions in mitochondrial DNA. These genetic lesions alter mitochondrial oxidative phosphorylation, with a reduction in energy produced for cell activity. Renal disease may be the first sign of mitochondrial cytopathy, or it may appear together with neurological and neuromuscular signs. Fanconi's syndrome, a benign sign of renal tubulopathy, is particularly frequent in newborns with mitochondrial cytopathy, whereas tubulointerstitial nephropathy, which affects infants and adults, is more serious because it develops into terminal uremia. Findings of hyperlactatemia and reduced enzymatic activity on the respiratory chain in tissue biopsies are of diagnostic significance in mitochondrial cytopathy. A breakthrough is being made in our understanding of genetic alterations in mitochondrial DNA, and with future therapy, the kidney, a target organ, may be safeguarded.