Oxidative phosphorylation (OXPHOS) diseases can be caused by mutations in nuclear genes or mitochondrial DNA (mtDNA) genes. mtDNA mutations include complex mtDNA rearrangements in which large segments of mtDNA are duplicated or deleted and point mutations in which single nucleotide substitutions occur within transfer RNA (tRNA) genes, ribosomal RNA (rRNA) genes, or mitochondrial genes encoding OXPHOS polypeptides. Although over 30 pathogenic mtDNA point mutations and over 60 different types of mtDNA deletions are known (Shoffner and Wallace, 1995; Wallace et al., 1994), only a subset of these mutations are associated with cerebellar ataxia. This review focuses on the clinical, biochemical, and genetic features of OXPHOS diseases caused by mtDNA mutations in which ataxia is a common manifestation.