A handful of preventable health-risk behaviors-violence, substance use, suicide, and sexual activity-are responsible for much of the mortality and morbidity experienced in adolescence and early adulthood. Adolescents' participation in many of these health-risk behaviors has changed in recent years. Newspapers report increases in marijuana use among high school students one day and declines in their sexual or criminal activity another. Because changes in the prevalence of specific health-risk behaviors vary, some increasing and some declining, shifts in adolescents' overall exposure to health-risks are difficult to pinpoint. While it is well established that many risk behaviors co-occur changes in the extent and patterns of multiple risk-taking are unknown.