Our institute is involved in mitochondrial DNA diagnostics and research of mitochondrial DNA alterations in rare diseases since 1999. Mitochondrial diseases comprise a group of rare diseases with a very broad phenotypic presentation, including diseases with variable progression and with both childhood- and adult-onset presentation. The common mechanism underlying this disease group is a deficiency of energy-pathways either encoded by the mitochondrial DNA or the nuclear DNA. In recent years our department has been investigating the phenotypic and genotypic variability of MELAS-syndrome, the molecular background of Leigh-disease and the genetic elucidation of maternally inherited deafness. Our biobank of mitochondrial diseases comprising more than 400 samples is an excellent source for the study of phenotype-and genotype variability in mitochondrial diseases. We primarily aim to attract students with a clinical focus also interested in the laboratory background behind diseases.