Despite minimum-purchase-age laws, young people regularly drink alcohol. This study estimated the magnitude and costs of problems resulting from underage drinking by category-traffic crashes, violence, property crime, suicide, burns, drownings, fetal alcohol syndrome, high-risk sex, poisonings, psychoses, and dependency treatment-and compared those costs with associated alcohol sales. Previous studies did not break out costs of alcohol problems by age. For each category of alcohol-related problems, we estimated fatal and nonfatal cases attributable to underage alcohol use. We multiplied alcohol-attributable cases by estimated costs per case to obtain total costs for each problem. Underage drinking accounted for at least 16% of alcohol sales in 2001. It led to 3,170 deaths and 2.6 million other harmful events. The estimated $61.9 billion bill (relative SE = 18.5%) included $5.4 billion in medical costs, $14.9 billion in work loss and other resource costs, and $41.6 billion in lost quality of life. Quality-of-life costs, which accounted for 67% of total costs, required challenging indirect measurement. Alcohol-attributable violence and traffic crashes dominated the costs. Leaving aside quality of life, the societal harm of $1 per drink consumed by an underage drinker exceeded the average purchase price of $0.90 or the associated $0.10 in tax revenues. Recent attention has focused on problems resulting from youth use of illicit drugs and tobacco. In light of the associated substantial injuries, deaths, and high costs to society, youth drinking behaviors merit the same kind of serious attention.