The past two decades are considered as the golden age of the clinical research of mitochondrial DNA. The number of disease-associated pathologic variants is still expanding; the available knowledge about the entities caused by the abnormalities of the mitochondrial DNA is gradually increasing. The inheritance of the mitochondrial DNA exhibits maternal transmission; the properties are different from the nuclear genome in many respects. Albeit the establishment of correct diagnosis of several mitochondrial diseases still means diagnostic challenge, more and more entities can be identified due to the available molecular biology methods. Nowadays, significant progress of mitochondrial medicine can be observed in relation to several medical subspecialties; thus, mitochondrial gastroenterology, endocrinology, otology, ophthalmology, nephrology, hematology, oncology, reproductive medicine and psychiatry have been partially separated as the more or less circumscribed territory of the specific subspecialty. Besides the short overview of the general aspects of the mitochondrial medicine the present review provides an outlook to these chapters.