ABSTRACT. Objective: Twelve-step mutual help groups such as Alcoholics Anonymous (AA) rely heavily on social interactions and support to reduce drinking, but little is known about how individual differences in social behavior tendencies, such as adult attachment, affect 12-step group engagement and resulting benefi ts. This prospective study investigated relationships between the anxiety and avoidance dimensions of adult attachment and subsequent 12-step meeting attendance, program behaviors, sponsorship, and alcohol use. Method: Early 12-step group affi liates (N = 253) were recruited from community-based AA and from outpatient treatment. Participants completed baseline interviews that included the Relationship Questionnaire, measures of motivation and professional treatment, and measures of 12-step meeting attendance, practices, and sponsorship. Follow-up interviews were conducted at 3, 6, 9, 12, 18, and 24 months. Results: At baseline, participants reported elevated attachment anxiety relative to a college population. Lagged analyses demonstrated that, as predicted, high attachment avoidance was related to lower rates of 12-step meeting attendance, practice of behaviors prescribed by 12-step organizations, and lower probability of acquiring a sponsor. Attachment anxiety did not predict any of these aspects of subsequent 12-step group engagement. Contrary to predictions, baseline attachment avoidance did not moderate the relationship between early sponsorship and alcohol use. Conclusions: Findings support the hypothesis that social demands of behaviors prescribed by 12-step groups may deter high-avoidance individuals from fully engaging in them. Perhaps because of instability in attachment avoidance in this population, however, baseline attachment avoidance did not predict drinking outcomes or moderate sponsor benefi ts. (J. Stud. Alcohol Drugs, 72, 854-863, 2011) (Finney et al., 1999;Kelly et al., 2006;Timko et al., 2000;Tonigan et al., 1996b). The 12-step program at the core of AA has been extended to other popular organizations such as Narcotics Anonymous. Benefi ts of 12-step group engagement are explained by a combination of 12-step-specifi c mechanisms (Kelly et al., 2010b;Robinson et al., 2007) and common change mechanisms (e.g., Forcehimes and Tonigan, 2008). Problem drinkers do not respond uniformly to 12-step groups; however, dropout rates are high (e.g., Kelly and Moos, 2003;Thurstin et al., 1987), and a substantial proportion of those who do attend meetings nevertheless report continued drinking and illicit drug use (e.g., Tonigan and Rice, 2010). These fi ndings highlight the importance of identifying the characteristics of problem drinkers that predict 12-step group affi liation and degree of engagement.Few consistent predictors of affi liation with 12-step organizations have been identifi ed. The most robust fi nding has been the positive association between alcohol problem severity and group engagement: greater alcohol problem severity predicted both initiation of group affi liation (Emric...