Aims: To seek a level of uniformity and consistency in the type of data or variables collected to allow cross-study comparison and ease in meta-analyses of adolescent treatment studies. Design: The rationale for adoption of such a core set of variables for adolescent treatment research, the main categories and specific types of variables, methods for collecting these variables, including the use of specific instruments are reviewed and discussed. Findings: There is a relatively small number of adolescent treatment outcome studies. Between studies, there are highly variable methodologies, including differences in how outcome or treatment success is measured, differences in ascertainment in substance use, differences in the measurement of non-substance use variables such as social and academic functioning, poor follow-up rates and a lack of comparison groups in many studies. Conclusions: Differences in the types and collection of baseline and outcome variables and the need to achieve some level of uniformity across adolescent substance use disorders (SUD) treatment studies suggest that investigators interested in adolescent treatment outcome research should develop a set of 'core variables' that are relatively consistent, or at least comparable, across studies.