The purpose of this study was to obtain evidence regarding the validity and reliability of an instrument to measure the self-reported competencies of interprofessional care in interprofessional education programs. Five hundred and eighty-four students and clinicians in Canada and New Zealand who were registered in 15 interprofessional education undergraduate, postgraduate, and continuing professional development programs completed the Interprofessional Collaborative Competency Attainment Survey (ICCAS) using a retrospective pre-test/post-test design. Factor analyses showed the presence of two factors in the pre-program items and one factor in the post-program items. Tests conducted provided evidence in support of the validity and reliability of the ICCAS as a self-assessment instrument for interprofessional collaborative practice. Internal consistency was high for items loading on factor 1 (α = 0.96) and factor 2 (α = 0.94) in the pre-program assessment and for the items in the post-program assessment (α = 0.98). The transition from a two factor solution to a single factor structure suggests interventions influence learners’ understanding of interprofessional care by promoting the recognition of the high degree of interrelation among interprofessional care competencies. Scores on the ICCAS are reliable and predict meaningful outcomes with regard to attitudes toward interprofessional competency attainment.