This study analyzed six waves of panel data from the National Longitudinal Survey of Youth (NLSY). These analyses were conducted to test the stability of self-reported lifetime use and age of onset. Intraclass correlation coefficients (ICCs) indicated that the stability of age of onset reports decreased with longer time frames between follow-ups. The percentage of youths who had discrepancies in self-reported ever use of alcohol at 2-year follow-up ranged from 15 percent to 35 percent. Higher discrepancy rates were found for males and younger respondents. Differences in report stability as a function of race/ethnicity were minimal. Questions related to lifetime use and age of onset have implications for the study of lifetime trajectories of use and the timing of prevention programs. Tables and references (Published Abstract)