Abstract We sought to characterize attrition-related characteristics of three subgroups of adults (i.e., early dropouts, late dropouts, treatment completers) who had participated in a marijuana-dependence treatment outcome study involving two alternative forms of outpatient group counseling. Early dropouts were younger, earned less income, were more likely to rent rather than own their domiciles, were less able to pay bills, and had a higher level of psychological distress than was the case with treatment completers. Late dropouts and completers were quite similar on a number of measures (e.g., age, income, home ownership, ability to pay bills, psychological stress level, confidence in being abstinent in the future), yet the lower rates of abstinence in the late dropouts largely resembled the treatment outcomes of early dropouts. The findings suggest that attrition prevention in the early phase of counseling ought to focus on motivational ambivalence as well as assisting the client in dealing with schedule conflicts or financial impediments to continued involvement. In the later stage of counseling, attrition reduction is more likely to be accomplished through efforts to better understand and address the client's dissatisfaction with treatment components delivered at that stage.