Background: Patient participation in treatment and care is often encouraged and is desirable because of its proven positive impact on treatment, quality of care and patient safety. Aims: To develop an instrument to measure patient participation in health care and to investigate the measurement properties of the Patient Participation Questionnaire (PPQ). Methods: A literature review was conducted to develop a model of patient participation. The PPQ was constructed consisting of 17 items organized into four subscales. Psychometric evaluation of factor structure, convergent construct validity by hypothesis testing and analyses of internal consistency using Cronbach’s alpha were performed on data from a hospitalised mixed group of patients with cardiac disease, pulmonary disease and cancer (N=378 patients). Results: Confirmatory factor analysis did not show a clear model fit, which is why an exploratory factor analysis was performed, suggesting a different four subscale structure consisting of a total of 16 items. The four subscales were labelled Shared decision power, Adapted and individualized knowledge, Collaboration and Human approach. There were strong ceiling effects on all items. Analysis of convergent construct validity showed a moderate correlation (0.59) between the PPQ and another instrument measuring patient participation. Internal consistency for the total PPQ score was high: 0.89. Conclusion: In a mixed group of patients with cardiac disease, pulmonary disease and cancer, the PPQ showed promising psychometric properties in terms of factor structure, convergent construct validity and internal consistency. The PPQ may be used to shed light on the experience of patient participation and guide quality improvements.