Patient-centeredness is one of the most important quality and outcome criteria in health care. Health care organizations are continually searching for approaches that will enable them to establish sustainable patient-centeredness in their daily practice. Existing approaches frequently focus on interaction between patient and health care professional (external participation). However, this is often not sufficient; other elements, such as good teamwork among the health care professionals (internal participation), are also essential. The model of integrated patient-centeredness differentiates between these two participations forms, both of which are explored from a patient and health care professional perspective in our study. The aim of the study was to confirm the model from the viewpoint of staff and patients. To this end we conducted a multi-center cross-sectional study consisting of a patient and staff survey to assess internal and external participation and patient-centeredness. A total of 15 rehabilitation clinics were involved, with 272 staff members and 536 patients included in the final analysis. Although evaluation was positive (mainly slightly above the middle of the scale), there was potential for improvement for both types of participation. Internal and external rating differed between patients and health care staff, with the first group assessing internal significantly better and external lower than the second group. The low to middle correlation of both types, as well as the correlation and regression with patient-centeredness, confirmed the model of integrated patient-centeredness. The model underlines the importance of both participation forms for patient-centeredness, as well as their interdependence. Further studies are needed in order to verify the impact of internal and external participation, as well as that of further possible dimensions of patient-centeredness, on clinical and functional outcome criteria.