The study was conducted under the auspices of the Pompidou Group of the Council of Europe. The analysis concluded that drawing together data from several indicators can produce a useful assessment of drug abuse. However, the agency-based data must be complemented by surveys and other studies of drug abuse in the populations concerned. The members of the expert group recommend that a single organizational unit integrate and analyze data and epidemiological studies and discuss different models of how such a unit can be achieved. Improvement in the consistency and quality of the data is essential if policies are to be based on a sound understanding of trends in drug abuse. 17 references. (Author abstract modified)