Background During the last few years there has been an increased interest of researchers in the field of substance dependencies for the use of standardized assessment instruments and for cross-national comparative research. This interest has been stimulated by the understanding that the evaluation of the preventive efforts can be enhanced through the measurement and standardization of factors associated with substance use and treatment outcome. Moreover, a better insight into substance use problems and into the effectiveness of prevention and treatment initiatives can be gained through collaborative studies among European countries. The European Commission has stimulated and continues to promote collaborative research and networking among European countries through the funding of joint multicenter programs. A couple of standardized instruments to be used in different sociocultural contexts exist in Europe for the assessment of substance-dependent individuals. The available instruments, however, are restricted mainly to items related to core demographic and drug use data (United Nations, WHO, Pompidou Group ‘First Treatment Demand Protocol’). At present it has been recognized by the scientific community that substance dependencies are a multidimensional phenomenon that should be approached as such. What has been missing in the available instruments in Europe is this aspect of multidimensionality. During a workshop on clinical epidemiology organized by AIAR in January 1993, the need to work towards the development of a uniform standardized multidimensional instrument for the assessment of substance abuse clients in Europe was for the first time expressed by the authors of this report. Developments followed quite rapidly. In a workshop, organized a few months later by COST-A-6 on ‘Evaluation Methods in Substance Abuse’in Zurich (Mai 1993), a coordinating group was constituted for the development of the European version of the Addiction Severity Index (ASI)[1]. The group comprised members from 5 European countries (Germany, Greece, Holland, Italy, Switzerland) that already had some experience using the ASI1. Since then, clinicians and reasearch-ers from a number of other European countries (Norway, Austria, Ireland, Portugal) have expressed their interest in the development of this European instrument. During 1993 and 1994 members of the group worked in collaboration, partly supported by COST-A-6, to produce the adaptation of the ASI and its guide to the European situation. Both the interview schedule (EuropASI) and its guide for training and administering EuropASI