This manuscript evaluates the effects of enactment of state laws that required safety belt use in various U.S. states between 1986 and 2000.Safety belt use was assessed using nationally representative cross-sectional samples of high school seniors; evaluation of the effects of laws used data from over 2,000 high school seniors before and about 3,300 after the laws took effect in 20 states.Belt use was found to increase significantly between 1986 and 2000, and the laws contributed significantly to that increase. Increases were similar for students differing by gender, race/ethnicity, parent education, grades, truancy, evenings out per week, miles driven per week, and an index of illicit drug use.The data show that although the laws have increased belt use, use is not universal and continued efforts are needed.This study shows that many teenagers fail to use belts when there is a secondary use law; an implication is that primary laws would be more efficacious in increasing use among this vulnerable population.