BACKGROUND: Although the presumption in health services literature has been that integrated delivery systems (IDSs) should improve the coordination of care, the benefits have not yet been well established through empirical research. PURPOSES: This study assesses whether receiving care from providers who belong to the same IDS improves patient-perceived coordination of care; concurrently, we develop a new approach for assessing the performance of IDS. METHODOLOGY/APPROACH: A study was conducted of 222 patients who received primary unilateral total knee arthroplasty at a large IDS' acute care hospital. To isolate the effects of provider membership, we enrolled patients who received surgery from the same surgical department in the same acute care hospital in the IDS. We used baseline and 6-week postoperation patient surveys to assess the impact of the participation of the patients' providers in the IDS on patient-perceived coordination of care. FINDINGS: We found no consistent effects of IDS membership on patient-perceived coordination of care. Patients with in-network rehabilitation care experienced fewer problems than patients with out-of-network rehabilitation care did, while patients with in-network home care experienced more problems than patients with out-of-network home care did. Membership of a patient's primary care physician had no observed effects. PRACTICE IMPLICATIONS: Health care managers and administrators need to undertake a realistic examination of the care-coordinating mechanisms that exist in their IDS. This study has shown that the integration of financial, contractual, and administrative processes is not enough to improve care from the patient's perspective; to improve care, it is advised that an IDS take a patient-centered approach in its design and implementation. We discuss potential reasons for uneven integration of IDS, particularly with respect to the lack of coordinating mechanisms, and argue for the usefulness of the approach developed here for assessing IDS performance over time.