ABSTRACT—High rates of teen pregnancy and sexually transmitted disease (STD) are important problems in the United States. Curriculum-based sex and STD/HIV education programs have been proffered as a partial solution. This article reviews evaluations of the impact of such programs that met specified criteria and finds that about two thirds of programs had a significant impact on behavior. The proportion having a negative impact was less than expected by chance. Those having a positive impact had such effects as delaying the initiation of sex, reducing the frequency of sex or the number of sexual partners, and increasing the use of condoms or other contraceptive methods. Positive findings were robust across different groups of youth and replication of programs in different locations. Programs with 17 specific characteristics were much more likely to be effective than programs without these characteristics. These programs alone cannot dramatically reduce teen pregnancy and STD, but they can contribute to the reduction of those problems.