The Youth Risk Behavior Surveillance System (YRBSS) is an epidemiologic surveillance system established by the Centers for Disease Control and Prevention (CDC) to monitor the prevalence of youth behaviors that most influence health. The 2005 Youth Risk Behavior Survey (YRBS) is one component of the YRBS. The 2011 National Youth Behavior Risk Survey (YRBS) is a school-based survey that provides data representative of 9th through 12th grade students in public and private schools in the United States. Since 1991, the YRBS has been conducted every two years by the Centers for Disease Control and Prevention (CDC). The national YRBS is one component of a larger surveillance system called the Youth Risk Behavior Surveillance System (YRBSS) that monitors six priority health-risk behaviors that contribute markedly to the leading causes of death, disability, and social problems among youth and adults in the United States. The 2011 National YRBS data set contains 207 variables administered to 15,425 respondents. Data were collected on the following priority risk behaviors among youth including: sexual behaviors that contribute to unintended pregnancy and sexually transmitted diseases, including HIV infection; behaviors that contribute to unintentional injuries and violence; alcohol and other drug use; tobacco use; unhealthy dietary behaviors; and inadequate physical activity. The YRBS also measures the prevalence of obesity and asthma among youth and young adults.