We compared school-based abstinence-only programs with those including contraceptive information (abstinence-plus) to determine which has the greatest impact on teen pregnancy. The United States has one of the highest rates of teen pregnancy in the industrialized world. Programs aimed at reducing the rate of teen pregnancy include a myriad of approaches including encouraging abstinence, providing education about birth control, promoting community service activities, and teaching skills to cope with peer pressure. We systematically reviewed all published randomized controlled trials of secondary-school-based teen pregnancy prevention programs in the United States that used sexual behavior, contraceptive knowledge, contraceptive use, and pregnancy rates as outcomes.