The New Jersey Substance Abuse Treatment Campus was funded to assess the feasibility of establishing a new model for delivering substance abuse treatment services and to serve as a research laboratory for conducting comparative evaluations of those services. The 350-bed campus was designed to improve treatment effectiveness by providing special services needed by underserved populations, and reduce treatment costs by serving large numbers of clients, centralizing services, and sharing facilities. First-time clients who met preliminary eligibility requirements during phone screening were randomly assigned to therapeutic community and chemical dependency programs. We used data collected on 1,573 adults who were ultimately accepted for admission to analyze treatment refusals and attrition during the 25 days after admission. Only 6.4% of the clients refused admission when informed of their treatment assignment. Planned duration of the residential phase of treatment, gender, and language spoken (English/Spanish) interacted with one another and differentially predicted treatment refusal/attrition. These findings may be useful for understanding treatment refusal and attrition in substance abuse treatment programs.