The current study examined the effectiveness of Matrix outpatient stimulant treatment. We associated 146 subjects' in-treatment abstinence data, treatment lengths, and weekly treatment activities to their 6-month abstinence outcomes as part of an interim analysis of a NIDA treatment demonstration project. Results indicated that the pretreatment subject characteristics of ethnicity and drug of choice significantly associated with treatment outcome using Matrix model treatment. Findings also demonstrated a treatment dose/abstinence response such that those who received longer Matrix treatment episodes demonstrated better abstinence outcomes. Further, in-treatment abstinence status and treatment length significantly associated with drug use status at follow-up. This set of findings provides evidence for the value of Matrix treatment and allows for these outcome data to be compared with reports on recent psychosocial treatments for stimulant dependence. This study also provides direction for evaluating longer term effectiveness for these types of drug treatments.