Clinician training and supervision are needed to transfer evidence-based practices to community-based treatment organizations. Standardized patients (SPs) are used for clinician training and evaluating. However, to be effective for substance abuse counselors, SPs must realistically portray substance abuse treatment clients. The current study assessed authenticity of SPs as substance abuse treatment clients. Twenty-one substance abuse counselors interviewed SP(s) with differing profiles. Counselors provided quantitative and qualitative ratings of SP authenticity. Counselor responses to the study procedures were analyzed as well. Quantitative results include high-authenticity ratings for the SPs but counselors' subjective responses varied. Counselor's rated the experience of participating in the study positively and provided constructive comments for future applications of this methodology. Results support future work on SPs as teaching and evaluation tools in substance abuse counseling. Findings also illustrate the need to refine definitions of authenticity for SPs as substance abuse clients. (Contains 4 tables.)