Objective: The purpose of this research was to evaluate the effectiveness of a comprehensive, strengths-based model of case management for clients in drug abuse treatment. Method: 503 volunteers from residential or intensive outpatient treatment were randomly assigned to one of three conditions of Iowa Case Management (ICM) plus treatment as usual (TAU), or to a fourth condition of TAU only. All were assessed at intake and followed at 3, 6, and 12 months. Results: Clients in all four conditions significantly decreased substance use by 3 months after intake and maintained most gains over time. However, the addition of ICM to TAU did not improve substance use outcomes. Conclusion: Overall, the addition of case management did not significantly improve drug treatment as hypothesized by both researchers and clinicians. Some results were mixed, possibly due to the heterogeneous sample, wide range of case management activities, or difficulty retaining participants over time. (Contains 6 tables.)