[영문]To examine costs and monetary benefits associated with substance abuse treatment.Primary and administrative data on client outcomes and agency costs from 43 substance abuse treatment providers in 13 counties in California during 2000?2001.Using a social planner perspective, the estimated direct cost of treatment was compared with the associated monetary benefits, including the client's costs of medical care, mental health services, criminal activity, earnings, and (from the government's perspective) transfer program payments. The cost of the client's substance abuse treatment episode was estimated by multiplying the number of days that the client spent in each treatment modality by the estimated average per diem cost of that modality. Monetary benefits associated with treatment were estimated using a pre?posttreatment admission study design, i.e., each client served as his or her own control.Treatment cost data were collected from providers using the Drug Abuse Treatment Cost Analysis Program instrument. For the main sample of 2,567 clients, information on medical hospitalizations, emergency room visits, earnings, and transfer payments was obtained from baseline and 9-month follow-up interviews, and linked to information on inpatient and outpatient mental health services use and criminal activity from administrative databases. Sensitivity analyses examined administrative data outcomes for a larger cohort (N=6,545) and longer time period (1 year). On average, substance abuse treatment costs