Substance abuse treatment clients often present other severe mental health problems that affect treatment outcomes. Hence, screening and assessment for psychological distress and personality disorder are an important part of effective treatment, discharge, and aftercare planning. The Millon Clinical Multiaxial Inventory-II (MCMI-II) frequently is used for this purpose. In this paper, several issues of concern to MCMI-II users are addressed. These include the extent to which MCMI-II scales correspond to DSM-III-R disorders; overdiagnosis of disorders using the MCMI-II; accuracy of MCMI-II diagnostic cut-off scores; and the clinical utility of MCMI-II diagnostic algorithms. Approaches to addressing these issues are offered.