The economic impact of disease and injury has most often been calculated by examining the costs associated with the prevalence of the impairments in the reference year. An alternative accounting approach is to assign all disease costs to the year of incidence, an approach which entails present-valuing to the year of incidence both health care expenditures and lost productivity. The incidence approach is the more appropriate for gauging the economic gains achievable through prevention, immediate rehabilitation, and arresting progression. Incidence-based costs have been estimated for the United States in 1975 for cancer, coronary heart disease, motor vehicle injuries, and stroke. A noteworthy finding is the relative economic importance of motor vehicle injuries, which frequently have been overlooked in the ordering of public health expenditure priorities. After cancer, which generated approximately $23.1 billion in present-valued costs in 1975 (discounted at 6 per cent), motor vehicle injuries and coronary heart disease constitute the next most expensive conditions--having generated estimated annual costs of $14.4 billion and $13.7 billion, respectively. Stroke, at $6.5 billion, follows in economic importance.