Preventive gerontology is the study and practice of those elements of lifestyle, environment, and health care management that will provide the maximal longevity of highest quality for individuals and the population. As such, it focuses on a personalized hygiene agenda that varies in its emphasis according to a person's age, sex, and risk factor profile. It includes a matrix of strategies relating to diet, exercise, and the avoidance of substance abuse and adverse environmental exposure. Preventive gerontology carries differential emphases according to the life stage of a person, featuring long-term, low-cost, and low-risk lifestyle strategies in youth and middle age (generally to age 75) and more short-term, low-risk interventions in old age (> 75), especially secondary prevention, according to individualized estimates of risk, cost, and benefit. The aggregate effect of widespread application of this approach--especially insofar as it is coupled with a rising level of education and continued psychosocial development--will be progressive congruency between usual and successful aging. A by-product will also be an ever-advancing median age of the population and, inevitably, a growth in long-term health and social service needs. Responsible planning for this consequence of success in the 21st century will require a rededication of North Americans to care for those in need regardless of age.