Background: Research evidence that shows the effectiveness of treatment in therapeutic communities for addicts and allows international comparisons to be made is rare in the Czech Republic. “The Treatment Outcome Evaluation of Therapeutic Communities for Drug Addicts” is the first prospective research study in the Czech Republic which looks into the effectiveness of drug treatment in therapeutic communities. Aim: The aim of the study is to evaluate the changes in clients’ substance use, offending, personal and social functioning, and quality of life one year after the completion of treatment. Methods: The data were collected using structured interviews administered to clients of therapeutic communities. The study compares changes in the clients’ problem behaviour within 30 days prior to treatment and within 30 days of one year after the completion of treatment. The Maudsley Addiction Profile, complemented with other measures, was used as the main research instrument. Sample: The study sample comprises 176 drug users who entered treatment in residential therapeutic communities in 2007 and 2008. At a one-year follow-up data were obtained from 77.8 % of the clients (N = 137). Four therapeutic communities participated in the study. Results: A significant increase in abstinence from methamphetamines, opiate drugs, and benzodiazepines was observed at the follow-up one year after the end of treatment. While prior to treatment 13.8 % of the clients abstained from all the study drugs, at the one-year follow-up it was 89.7 % of the clients. A significant drop in the level of offending was further ascertained. While 73.2 % of the clients engaged in criminal activities had committed 12,728 offences prior to treatment, one year after the completion of treatment offending was reported by 9.6 % of the clients; the number of criminal offences was reduced to 478. Alcohol use recorded only a minor improvement. 31.3 % of the clients were found to consume alcohol in a harmful manner at the one-year follow-up. Those clients who had completed treatment showed better outcomes than those who had dropped out. Conclusion: The clients of therapeutic communities show very good treatment outcomes, despite the severity of their drug-related, social, and other problems. Treatment in therapeutic communities significantly reduces substance use and criminal behaviour. The finding that one third of clients engage in the harmful use of alcohol following their treatment in a therapeutic community is a cause for concern.

Key words: therapeutic community – treatment outcome – drug use – crime – alcohol use