Although increasing disability is a common concomitant of old age, several interventions may prevent or delay disabling diseases. The "young-old" differ little from middle-aged people in their potential to benefit from many interventions. As age increases, clinicians need to become increasingly circumspect about interventions with a potential for harm and for benefit. By carefully weighing existing disease burden, the state of our knowledge about prevention, and patient values, however, clinicians may develop a reasonable preventive program in consultation with the patient and, where there is diminished competence, relevant family members. As we gain new knowledge about genetic and other risk factors, we may be able to more accurately and effectively target preventive services to maximize benefits and minimize harms in the population as a whole.