Substance use among youth and young adults continues to pose a variety of public health challenges. Young people who use opiates (heroin) and methamphetamine are more likely to have high risk sexual and injection practices, as well as more likely to be HIV+. Drug use among youth may be associated with a variety of problems including family trauma, academic difficulties, mental and physical health problems, sexual abuse, incarceration, poor peer relationships and violence. Youth in Northern California who are at risk for drug use, HIV and related health problems need to be better understood and targeted for prevention programs. The primary objective of SYNC is to conduct a cross-sectional study of a multi-ethnic sample of substance-using youth, 14-25 years old. This will be done in two phases.