BACKGROUND: Patient care ownership improves accountability, clinical skills, and quality of patient care among resident physicians, but appears to be gradually eroding. Research is limited by the lack of a reliable, objective measure of ownership. OBJECTIVE: To validate the Patient Care Ownership Scale, an instrument that measures decision ownership among internal medicine residents. DESIGN: Multi-institutional, cross-sectional study using a 66-item, online survey that queried residents on ownership's key constructs (advocacy, responsibility, accountability, follow-through, knowledge, communication, initiative, continuity of care, autonomy, self-efficacy, and perceived ownership) as well as mood and burnout. PARTICIPANTS: Internal medicine residents in five geographically diverse residency programs completing an inpatient rotation. MAIN MEASURES: We performed exploratory and confirmatory factor analysis in two randomly split groups to evaluate for subscales and inform item reduction. We conducted reliability testing with Cronbach's α. We performed bivariate analyses to examine construct validity and identify correlates of ownership. KEY RESULTS: Of the 785 eligible residents, 625 completed the survey (80% response rate); we included responses from 563 in the analysis. We identified three factors corresponding to assertiveness, conscientiousness, and confidence or perceived competence. After iterative item reduction, the 13-item ownership scale demonstrated good reliability (Cronbach's α = 0.82). Convergent validity was supported by a significant association with perceived ownership (eliminated from the final scale) (r = 0.67, p < 0.001). There was a positive association between ownership and training level (p < 0.01) and prior experience in the intensive care unit (p < 0.001). There were significant, inverse relationships between ownership and self-defined burnout (r = − 0.24, p < 0.001), depression (r = − 0.22, p < 0.001), detachment (r = − 0.26, p < 0.001), and frustration (r = − 0.15, p = 0.02), and significant positive associations between ownership and feeling energetic (r = 0.29, p < 0.001), happy (r = 0.33, p < 0.001), and fulfilled (r = 0.34, p < 0.001). CONCLUSIONS: The Patient Care Ownership Scale is valid in diverse residency program settings. Medical educators and investigators can use our scale to assess interventions aimed at fostering ownership.