Sex and HIV education programs that are based on a written curriculum and that are implemented among groups of youth in school, clinic, or community settings are a promising type of intervention to reduce adolescent sexual risk behaviors. This paper summarizes a review of 83 evaluations of such programs in developing and developed countries. The programs typically focused on pregnancy or HIV/STI prevention behaviors, not on broader issues of sexuality such as developmental stages, gender roles, or romantic relationships. The review analyzed the impact programs had on sexual risk-taking behaviors among young people. It addressed two primary research questions: What are the effects, if any, of curriculum-based sex and HIV education programs on sexual risk behaviors, STI and pregnancy rates, and mediating factors such as knowledge and attitudes that affect those behaviors? What are the common characteristics of the curricula-based programs that were effective in changing sexual risk behaviors?