Cost pressures are driving the reorganization of the health care delivery system in the United States, causing health care delivery organizations to become larger and more diversified. These new health care delivery entities are arriving at the same time as a new approach to clinical care: commercial population-based medicine. This approach is sharing an increasing amount of space with the traditional physician-patient-based approach and offers strategies for managing a population's risk, demand, diseases, and outcomes. Although commercial population-based medicine strategies such as disease management may use many of the same tools as traditional public health approaches, they focus on the relatively short-term health needs of defined populations because of the underlying economic incentives facing payers. Population-based-medicine promises better use of resources and a systems approach to health care delivery, but it also presents the pitfalls of subversion by the needs of commercial companies, unanticipated adverse effects, and wide application without adequate preparation.