Molecular genetic studies are now bringing a new classification and new insights into already recognized mitochondrial encephalomyopathies. There are, however, numerous reports on an overlap pattern between mitochondriopathies. In addition, the link between the defect in oxidative phosphorylation (OXPHOS) in the brain and the specific neuropathological pattern is unclear. A better knowledge of nuclear mutations in mitochondriopathies and of the interactions between nuclear and mitochondrial genomes will probably allow new developments.