The project: In the years after the formal start of substitution maintenance treatment (SMT) in Slovenia in 1994, this treatment option has been implemented nation-wide. In the summer of 2006 the Slovene Minister of Health presented a call for proposals for an evaluation, using funds from the European Commission. The aim of this evaluation is to assist in improving the quality of SMT in Slovenia. The evaluation should explore the quality of SMT, its cost-effectiveness and its impact on patients. The Trimbos Institute (the Netherlands Institute of Mental Health and Addiction) was selected to do this evaluation in cooperation with the Faculty of Social Work of the University of Ljubljana. For several reasons, the cost-effectiveness analysis and the impact analysis were not considered feasible. This resulted in an adapted outline of this evaluation. In agreement with the Slovene Ministry of Health, the first analysis was changed in a qualitative exploration of aspects of management, organization and costs of SMT. The impact analysis was abandoned and replaced by detailed recommendations on how to monitor and evaluate the impact of SMT on patients in the future. The report: After a chapter describing the methods used, this report starts with presenting context information on SMT in Slovenia, including a description of the background and the current organization of SMT. Its rationale, aims, and the available evidence of effectiveness of SMT are briefly reviewed. We also included a qualitative force field analysis that gives an impression of the forces and interests influencing policy choices on SMT. The report continues with an assessment of the quality of SMT, based on several core items from the literature. Here we also included an analysis on patient satisfaction. Next, the results are presented of an indicative inventory of the efficiency of SMT. This was done by assessing the funds and expenditures, aspects of SMT management and some organizational issues. For a broader view on SMT, a selection of data from reference countries is briefly presented to enable a rough comparison between the Slovene situation, and that in four other EU countries. (Author' s abstract)