The United States National Youth Risk Behavior Surveillance System (YRBSS) was developed to provide data on health risk behaviors and the prevalence of obesity and asthma for representative samples of 9th through 12th grade public and private school students in the United States. Youth Risk Behavior Surveys (YRBS) are implemented at the national level by the Centers for Disease Control and at the state, territorial, tribal and local levels by area departments of health and education. Conducted every 2 years, the YRBS includes a national high school, local high school, and middle school questionnaire that collects information on physical inactivity, alcohol and illicit drug use, unhealthy diet, and behaviors that contribute to STDs, unintended pregnancies, injuries and violence. For the 2009 YRBS, 16,460 national questionnaires were completed in 158 schools and 42 state, and 20 local surveys were conducted with sample sizes ranging from 965 to 14,870.