This study used the National Longitudinal Survey of Youth and is the first to examine a 2-year report stability of substance use among adolescents while stratifying for gender, ethnicity, and age. This study examined lifetime use and age at onset report stability, and the internal consistency of reports while excluding nonusers and incident cases (respondents who may have initiated substance use between the two reporting periods) from the analyses. Report agreement of lifetime use for each substance was over 80% and was highest among alcohol users and lowest for cigarette and marijuana users. Report agreement was higher for female compared to male cigarette users. External consistency of lifetime use of cigarettes and marijuana was higher for whites compared to Hispanic or African American adolescents. Internal consistency was high but lifetime use reports were more stable than age at onset reports.