There is a considerable disparity between the number of individuals who need substance abuse treatment and the number who actually receive it. This is partly due to the fact that many individuals with substance use disorders do not perceive a need for formal treatment. Another contributing factor, however, is a discrepancy between the real and perceived cost of services. Although many cost evaluations of substance abuse treatment have been conducted from the treatment provider perspective, less is known about the client-specific costs of attending treatment (e.g., lost work and leisure time, transportation, out-of-pocket and in-kind payments). Concerns about financial and other barriers to participating in treatment have encouraged addiction researchers to more carefully consider these previously unmeasured costs. To address this information gap, we administered the Client Drug Abuse Treatment Cost Analysis Program (Client DATCAP) to 302 clients (representing a total of 302 outpatient and 142 inpatient treatment episodes) as part of a larger study examining the cost-effectiveness of interventions designed to improve treatment linkage and engagement in Dayton, Ohio. The value of a client's time accounted for the largest component of total cost (more than 59%). The cost per visit for outpatient clients ranged from $19 for outpatient methadone to $38 for intensive outpatient/aftercare treatment. The average cost per day of treatment for inpatient clients was $235. Policy makers and treatment providers now have a broader view of the opportunity cost of addiction treatment and can use this information to support initiatives for improved treatment access and delivery.