The purpose of this study was to develop and evaluate an interprofessional identity measurement instrument based on Extended Professional Identity Theory (EPIT). The latter states that interprofessional identity is a social identity superordinate to a professional identity consisting of three interrelated interprofessional identity characteristics: belonging, commitment and beliefs. Scale development was based on five stages: 1) construct clarification, 2) item pool generation, 3) review of initial item pool, 4) shortening scale length (EFA to determine top four highest factor loadings per subscale; 97 dental and dental hygiene students), and 5) cross-validation and construct validity confirmation (CFA; 152 students and 48 teachers from six curricula). Explained variance of the EPIS was 65%. Internal consistency of the subscales was 0.79, 0.81 and 0.80 respectively and 0.89 of the overall scale. CFA confirmed three-dimensionality as theorized by EPIT. Several goodness-of-fit indexes showed positive results: CFI = 0.968 > 0.90, RMSEA = 0.039 < 0.05, and SRMR = 0.056 ≤ 0.08. The factor loadings of the CFA ranged from 0.58 to 0.80 and factors were interrelated. The Extended Professional Identity Scale (EPIS) is a 12-item measurement instrument with high explained variance, high internal consistency and high construct validity with strong evidence for three-dimensionality.