DISEASE PREVENTION HAS ALWAYS BEEN THE PREferred option for promoting health and reducing disease rates. For many, this health argument is reason enough to invest in prevention, economics aside. Others, citing scarce resources, advocate a careful assessment of the costs and savings associated with prevention. It initially costs more to deliver preventive services; the savings the resulting health benefits will incur over time are less clear. Some reports claim that effective prevention programs would save the nation billions of dollars, while others predict the reverse. Economists and columnists have argued that prevention rarely saves money and is inherently no more cost-effective than disease care. For policy makers—caught between an economic crisis, pressure to defer new spending and seize control over escalating health care costs, and a promise to voters to make prevention part of health care reform—resolving whether prevention will help reduce spending is highly relevant. The question of whether prevention saves money is incorrectly framed. Health care, like other goods, is not purchased to save money. The dollar can be stretched further— more goods can be acquired—by optimizing economic value. The proper question for a preventive (or therapeutic) intervention is how much health the investment purchases. This is typically measured in terms of cost-effectiveness or cost-utility, the ratio between the cost of a service and its benefits. Some services cost relatively little per unit of health gain and represent good buys. Some are extremely good buys because they generate net savings, but such services are uncommon. Much of the nation’s enormous health care budget goes toward expensive tests and treatments that produce relatively little health gain per dollar. Services ordinarily are considered to have reasonable cost-effectiveness if they cost less than $50 000 to $75 000 per quality-adjusted life year (QALY), but payers routinely cover treatments that cost more than $100 000 per QALY. The occasional service that produces net savings is hardly a panacea for controlling spending. Through sheer volume, far more can be accomplished by curtailing lavish outlays on expensive, low-value services and investing more in high-value services that improve health at less cost (and may occasionally yield net savings). This redistribution in spending offers the greatest opportunity to save more lives with the same dollar. Prevention stands out among the cadre of interventions that combine good health outcomes with good economic value. Although disputes exist on the margins, this much is clear: 1. A core set of preventive services is effective. Hundreds of thousands of lives would be saved annually if people stopped smoking, lost weight, exercised regularly, and consumed a healthy diet. Support is also nearly universal for a package of effective clinical preventive services (eg, screening tests, immunizations) recommended by the US Preventive Services Task Force and other reputable groups. Improved implementation of this core package could greatly reduce the nation’s disease burden. By one account, increasing delivery of just 5 clinical preventive services would avert 100 000 deaths per year. 2. These evidence-based clinical preventive services offer high economic value. Whereas major disease treatments (eg, angioplasty) can cost $100 000 or more per QALY, most evidence-based preventive services offer a better value. For example, colonoscopy and other evidence-based screening tests for colorectal cancer cost less than $25 000 per QALY. Among 25 recommended preventive services, 15 cost less than $35 000 per QALY and 10 services cost less than $14 000 per QALY. 3. Among the core set of preventive services that offer high economic value, a subset yields net savings. The literature reports net savings from childhood immunizations, smoking cessation, and aspirin prophylaxis among patients at increased risk for cardiovascular disease. Smoking cessation counseling by clinicians, if not cost saving, is highly cost-effective (less than $5000 per QALY). 4. Some preventive services, like many disease treatments, offer poor economic value. Cost-effectiveness is poor when effectiveness is uncertain or, as happens with some preventive services, the absolute probability of benefit is low (eg, offering services to low-risk patients, frequent rescreening, and pursuing aggressive targets [eg, reducing lowdensity lipoprotein cholesterol levels to 100 mg/dL]).