The YRBSS included a national school-based survey conducted by the Centers for Disease Control, as well as State, territorial, and local school surveys conducted by education and health agencies. The survey was conducted among high school students during February-May 1999. Results showed that numerous high school students engaged in behaviors that increased their likelihood of death: 16.4 percent had rarely or never worn a seat belt, 33.1 percent had ridden with a driver who had been drinking alcohol during the 30 days preceding the survey, 17.3 percent carried a weapon during the 30 days preceding the survey, 50 percent had consumed alcohol during the 30 days preceding the survey, 26.7 percent had used marijuana during the 30 days preceding the survey, and 7.8 percent had attempted suicide during the 12 months preceding the survey. Substantial morbidity and social problems among young persons also resulted from unintended pregnancies and STDs, including HIV infection. In 1999, nearly 50 percent of high school students nationwide had engaged in sexual intercourse, 42 percent of sexually active students had not used a condom at last sexual intercourse, and 1.8 percent had injected an illegal drug. Two-thirds of all deaths among persons 25 years of age and younger resulted from only two causes, cardiovascular disease and cancer. Most risk behaviors associated with these two causes of death were initiated during adolescence. In 1999, 34.8 percent of high school students had smoked cigarettes during the 30 days preceding survey, 76.1 percent had not eaten a proper diet, 16 percent were at risk of becoming overweight, and 70.9 percent did not attend physical education classes daily. 11 references and 43 tables