In therapeutic community models for drug treatment, individual recovery is principally structured around group meetings and positive peer influences. Research shows that asocial group members with resistant behaviors and attitudes are at risk for poor treatment outcomes and have the potential to adversely impact the therapeutic group. To gain a better understanding of the asocial client's role in the larger treatment process, in-prison treatment data were used: (1) to model and confirm a two-factor solution of asociality consistent with the literature, and (2) to examine the relationship between asocial clients and treatment engagement for validation of the two-factor model. Exploratory analysis resulted in a three-factor solution representing behavioral responsivity, cognitive distortion, and social disassociation dimensions. Nested ANOVA (i.e., clients nested within prison programs) demonstrated that asocial levels (low, medium, and high risk) predicted treatment engagement. Furthermore, comparisons among asocial risk levels indicated that high asocial clients reported significantly lower engagement levels when compared with low and medium asocial clients. Copyright © 2012 John Wiley & Sons, Ltd.