Background: Long-term drug rehabilitation programmes are now recognised as being more effective than the ambulatory treatments, if one refers to the long-term abstinence. However, the majority of these programmes are open only to the patients abstinent from all substances. Consequently, detoxification units must be adapted to treat a broad variety of patients with individual needs. Objective: The aim of the present research was to characterise a French-speaking Swiss cohort of illicit drug users attending a newly opened "high-threshold" detoxification unit of the University Department of Adult Psychiatry, in Lausanne, Switzerland. Method: This prospective study was conducted between January 1998 and December 2000. During the first 3 years of activity, 550 consecutively admitted patients for a detoxification treatment in a 10-bed unit were submitted to a semi-structured interview assessing sociodemographic data, history and patterns of drug/alcohol consumption, number and type of previous treatments for drug-related problems, treatment completion and future therapeutic programme. Differences in means of continuous variables were calculated using Student's t-test. Chi-square statistics were employed to evaluate differences in proportions. Results: The mean age was 29.5 +or- 6.5 years. The majority of the patients were polydrug abusers, with opiate as a first choice. They had a drug-use history of 9.1 years mean and 507 had had at least one previous withdrawal experience. Half of the patients had previously experienced a therapeutic community for a stay of one to 6 month. The patients treated in our unit generally remained in the addiction network once they had entered it. A great proportion of the patients (311/550 - 56.5%) were planning to enter a therapeutic community after treatment, but only (161/550) 29.3% really did it. The majority of the patients ended the physical part of the withdrawal (negative urines). Over three years of observation, no changes over time were observed as far as the income resources, the type of drug consumption, the route of administration, the rehabilitation project nor the end of treatment mode are concerned. Conclusion: A medically assisted high threshold withdrawal programme in a hospital setting may reach a wide range of drug-dependent patients. As it facilitates medical monitoring and a more intensive psychosocial follow-up, it becomes a very useful tool for the integration and the stabilisation of the patients in a specific health network. These findings emphasise the need for detoxification clinics to be accessible to all patients, regardless of the state of their recovery process or the state of their motivation. Now patient-treatment matching is no more a static method but a dynamic process, which necessitates continuous evaluations and adaptations of the treatment to the patient's individual specificity. (PsycINFO Database Record (c) 2006 APA, all rights reserved) (journal abstract)