The National Treatment Outcome Research Study (NTORS) provides information about the pre-treatment behaviour, problems and social circumstances of a cohort of drug misusers admitted to addiction treatment services. It also includes information on self-reported offending following treatment, operational characteristics and interventions, and client outcomes. NTORS, the first national prospective study of treatment outcome among drug misusers to be conducted in the UK, began in 1995 and 54 treatment agencies in England participated in the study