Congress has used cost-effectiveness analyses in deciding that Medicare should cover selected secondary prevention services, such as screening for breast cancer and colon cancer. But the measure of cost per QALY is routinely ignored in decisions both about treatment for demonstrated disease and about primary prevention of disease. It is ignored, though, in entirely different ways. Medical treatments are paid for even if they are cost-ineffective; in fact, the Medicare program has been blocked from even considering cost-effectiveness in determining whether to cover the costs of treatment. For example, treatment of metastatic lung cancer may cost $800,000 per QALY, but it is typically provided. In sharp contrast, primary preventive services are often withheld even if they are highly cost-effective. For example, the Diabetes Prevention Program, a lifestyle-training program focused on exercise and nutrition that costs only $14,000 per QALY, is covered by only some health insurance plans; Medicare is not among them.