Chronic illness is the largest cause of death and source of health care costs in developed countries and has become a significant problem in developing countries as well. This paper begins with a review of past work in System Dynamics concerning populations with chronic illness. It then presents a generic model of illness in a population and its treatment and prevention, applied to the U.S. population. The model explains the rising prevalence of illness as well as responses to it, responses which include the treatment of complications as well as disease management activities designed to reduce the occurrence of future complications. The model shows how progress in complications treatment and disease management has slowed since 1980 in the U.S., largely due to a behavioral tug-of-war between health care payers and providers that has resulted in price inflation and an unstable climate for health care investments. The model is also used to demonstrate the impact of moving “upstream” by managing known risk factors to prevent illness onset, and moving even further upstream by addressing adverse behaviors and living conditions linked to the development of these risk factors in the first place.