There is an important need for adolescent-based tools to assess drug use. Several adolescent-based instruments have been developed in the United States. However, in French speaking countries, there are no standardized instruments available. The Adolescent Drug Abuse Diagnosis (ADAD) was translated and used to evaluate adolescent drug users in the French-speaking part of Switzerland. The ADAD is seen as an adequate tool for use in both clinical and research contexts. When used in a 4-year longitudinal study, this paper analyzed methodological aspects of the ADAD at several levels: assessment content and format, setting, and measurement of outcomes. This paper highlights observations made in using the ADAD. The ADAD instrument seems appropriate to collect detailed lifetime and current situation information, specifically for longitudinal and clinical studies where interpersonal relationship is more important. The interview content and format make the ADAD usable with adolescents and young adults, and with substance users and non-users. References