The current study examined the impact of a brief motivational interviewing (MI) intervention (Project CHAT) on alcohol consumption and drug use for high-risk teens in a primary care clinic that provides health care for underserved populations. Youth (N=42, 48% male) were screened, and those eligible completed a baseline survey. Baseline survey completers were randomly assigned to usual care or to an MI intervention and completed a 3-month follow-up survey. The sample (age 12 to 18 years) was 85.7% Hispanic or Latino, 9.5% African American, and 4.8% White. At the 3-month follow-up, Project CHAT teens reported less marijuana use, lower perceived prevalence of marijuana use, fewer friends who used marijuana, and lower intentions to use marijuana in the next 6 months, as compared to teens assigned to usual care. Providing this type of brief intervention is a viable approach to working with high-risk teens to decrease substance use.