Health initiatives suggest that adolescent substance use assessment may be beneficial as part of primary care to screen for early problematic behaviors. To examine the accuracy of such reporting, we compared the anonymous and confidential self-reports of 180 adolescents in a primary care setting. Matching samples to control for demographic variables, we found that adolescents were more likely to report marijuana use and substance use behaviors, such as selling drugs, when reporting anonymously vs. reporting confidentially. These results challenge the accuracy of confidential self-reports within this setting, and suggest further research is needed.