A multifactorial and growing crisis of health care systems in the developed world has affected medicine. In order to provide rational responses, some central concepts of the past, such as the definitions of health and disease, need to be updated. For this purpose physicians should initiate a new debate. As a point of departure the following definitions are proposed: Health is a dynamic state of wellbeing characterized by a physical, mental and social potential, which satisfies the demands of a life commensurate with age, culture, and personal responsibility. If the potential is insufficient to satisfy these demands the state is disease. This term includes sickness, illness, ill health, and malady. The described potential is divided into a biologically given and a personally acquired partial potential. Their proportions vary throughout the life cycle. The proposed definitions render it empirically possible to diagnose persons as healthy or diseased and to apportion some of the responsibility for their state of health to individuals themselves. Treatment strategies should always consider three therapeutic routes: improvements of the biologically given and of the personally acquired partial potentials and adaptations of the demands of life. These consequences favourably contrast with those resulting from the WHO-definition of health.