The relationship between quality of life and aging is difficult to describe with the usual epidemiological concepts like mortality. A functional approach is more important and meaningful for the analysis of the aging process. The ICIDH classification has the advantage of combining the diseases process itself and the consequences concerning functional limitations. Studies about the "active life expectancy" show that quality of life and life expectancy are two different dimensions of the aging process. For the purpose of prevention, it is important to demonstrate that preventive interventions could help reduce the number of years with functional limitations. Most of the epidemiological studies indicate that even lost functions could be restored. For these interventions, it is important to individualize the goals for preventive measures to balance physical and emotional needs of the elderly.