Should we measure blood cholesterol levels in all adults, or only in those at high risk of coronary heart disease (CHD)? Most men under the age of 35 years and women under the age of 45 years—roughly half the adult population—are at very low short-term risk of CHD. One consequence is that drug treatment to lower high blood cholesterol levels in the average young adult is an extremely expensive means of prolonging life; the estimated $1 million to $10 million per year of life is 100 to 1000 times the cost of other approaches. Individualized dietary treatment is somewhat cheaper but relatively ineffective. Another consequence of the low CHD risk in young adults is the greater likelihood that intervention may have harmful effects that outweigh the benefits. Meta-analyses of primary prevention trials in middle-aged men reveal an increase in non-CHD deaths among those randomized to cholesterol interventions, an unexpected finding that is more substantial than the decrease in CHD deaths. This raises the possibility that one or more of the cholesterol interventions could have very serious adverse effects among young adults, whose risk of non-CHD death is normally 100 times their risk of CHD death. We conclude that the policy of screening and treating high blood cholesterol levels in young adults is neither cost-effective, nor does it satisfy ethical standards requiring strong evidence that preventive interventions do more good than harm. Fortunately, cholesterol screening in young adults is also not necessary: most CHD events associated with high blood cholesterol levels in this population will not occur for decades and can be prevented by treatment that is begun in middle age. Cholesterol screening and treatment in young adults should be limited to individuals with known coronary disease or other unusual factors that place them at high short-term risk of CHD death.