Of the three published instruments that assess cultural issues in supervision, two have not been tested for convergent or discriminant validity, but one the Multicultural Supervision Inventory (MSI), has garnered initial empirical support (Pope-Davis, Toporek, Ortega, 1999; Pope-Davis, Toporek, Ortega-Villalobos, 2003). This study presents the refinement of the Multicultural Supervision Inventory (MSI; Pope-Davis, Toporek, Ortega, 1999), a measure of multicultural competence in supervision developed for use by both supervisors and supervisees. Data was collected from a diverse national sample of 176 supervisors and 424 supervisees in APA accredited internship training sites and academic programs, through self-report questionnaires hosted by a website. Participants completed a detailed demographic background and experience questionnaire, the MSI (Pope-Davis, Toporek, Ortega-Villalobos, 2003), the MCKAS (Ponterotto et al., 2002), the Working Alliance Inventories (Bahrick, 1990) and the Paulhus Deception Scale (Pauhlus, 1991). The hypothesis that multicultural competence in supervision was a multidimensional construct received empirical support based on the confirmatory factor analyses of a correlated two factor structure. Multi-group analyses indicated that there is limited evidence of the factorial invariance for the MSI across the supervisor and supervisee samples. The results also provided supportive evidence for the scale's reliability (Supervisor α=.90; Supervisee, α=.96). A discriminant validity test indicated a small significant relationship between the MSI and social desirability scores accounting for 6% of the variance, which required the control of this variable in additional construct validity tests. Convergent validity tests confirmed the hypothesized theoretical relationships, demonstrating significant positive relationships between MSI scores and multicultural counseling competence scores, supervisory working alliance scores, the amount of time and quality of discussions addressing cultural variables in supervision, supervisors' intentionality, direct guidance, and perceived importance given to multicultural issues in supervision, and multicultural training and experience. In closing, this study outlines the next steps in the construct validation of the MSI including studies involving matched supervision dyads, longitudinal data collection, and mixed methodology. Recommendations are also made for the use of the MSI as an empirically supported training tool to help supervisors and supervisees in their process of developing multicultural competence.