Malnutrition, sarcopenia and cachexia are three syndromes that are highly relevant for capacity, morbidity and mortality of the elderly. The term malnutrition denotes a deficit of macro- und micronutrients, while sarcopenia describes an age-associated loss of muscle mass and strength. In cachexia weight loss und changes in body composition are closely related to acute and chronic inflammatory co-morbidities. A wide array of possible causal factors is typical for all three entities. Inflammatory processes and changes in hormonal regulation are of prominent importance for sarcopenia and cachexia. The diagnosis of malnutrition, sarcopenia and cachexia requires, in addition to a special interest of the treating physician, a thorough knowledge of pathophysiology as well as the use of specific diagnostic methods. A better understanding of the causes of malnutrition, sarcopenia and cachexia will make it possible to use specific modes of treatment. Because of the demographic shift an increasing financial burden has to be faced by the public health system resulting from the growing expenditure needed for the care of affected patients. Additional studies are, therefore, necessary to develop new therapeutic options based on the pathophysiology of these three entities. This is especially important with regard to sarcopenia and cachexia.