Aims: This study investigates the relationship between attendance at Alcoholics Anonymous (AA) meetings prior to, during, and after leaving treatment, and changes in clinical outcome following inpatient alcohol treatment. Methods: A longitudinal design was used in which participants were interviewed at admission (within 5 days of entry), and 6 months following departure. The sample comprised 150 patients in an inpatient alcohol treatment programme who met ICD-10 criteria for alcohol dependence. The full sample was interviewed at admission to treatment. Six months after departure from treatment, 120 (80%) were re-interviewed. Results: Significant improvements in drinking behaviours (frequency, quantity and reported problems), psychological problems and quality of life were reported. Frequent AA attenders had superior drinking outcomes to non-AA attenders and infrequent attenders. Those who attended AA on a weekly or more frequent basis after treatment reported greater reductions in alcohol consumption and more abstinent days. This relationship was sustained after controlling for potential confounding variables. Frequent AA attendance related only to improved drinking outcomes. Despite the improved outcomes, many of the sample had alcohol and psychiatric problems at follow-up. Conclusions: The importance of aftercare has long been acknowledged. Despite this, adequate aftercare services are often lacking. The findings support the role of Alcoholics Anonymous as a useful aftercare resource.