The aim of this study was to investigate the process and outcomes of an inpatient drug and alcohol unit, the first ofits kind in Northern Ireland. The thesis includes a literature search exploring international prevalence rates, policy and practice and theories which influence research in the field. The study used a mixed method, longitudinal design incorporating preliminary exploratory structured interviews and a pilot study, followed by semi-structured baseline interviews using the Addiction Severity Index, the University of Rhode Island Change Assessment, the Coping Response Inventory and an environmental support questionnaire. Baseline numbers included 163· (99%) ofadmissions to the inpatient programme for a period of one year. A six month follow-up included 115 (70%) ofthe original respondents. The study found that a number ofbiopsychosocial, cognitive, behavioural and motivational factors appeared to be influential in treatment outcomes. Factors that were found to affect retention in treatment and reduction of post treatment lapses included: cognitive avoidance; employment and psychological status; levels of alcohol severity; anger, rage and violence issues, aftercare treatment services in the community; attendance in a 12 step programme and participation in ex-patient meetings. Motivation did not appear to be a major factor in client retention rates.