Up to 40% of medically ill patients suffer from clinically relevant depressive disorders, of which almost half can be classified as major depression. Some modern medical treatment procedures seem to increase the risk of depression. Quality of life as well as influences detrimental to the course of medical illness can be favourably influenced by a validated diagnostic approach and early careful therapeutic interventions. However, treating depressive disorders does not seem to exert a direct influence on the somatic prognosis. High depressive co-morbidity and burden of illness for both the individual and the society form a stark contrast to the obviously still insufficient diagnostic and therapeutic strategies in daily medical routine.