Although prior research has found differences in costs and financial performance across different types of hospital systems, there has been no systematic study of variations in patient quality of care or safety indicators across different systems. Our study examines whether five main types of health systems - centralized (CHS), centralized physician/insurance (CPIHS), moderately centralized (MCHS), decentralized (DHS), and independent (IHS) - as well as other hospital characteristics are associated with differences in quality of patient care. Data were assembled for 6 years (1995 - 2000) from multiple sources. We used 4 AHRQ risk adjusted inpatient quality indicators (IQIs) and 5 risk-adjusted patient safety indicators (PSIs) as dependent variables. Random effects models were used in the analysis.It was found that the IQI and PSI models have different patterns. In the IQI models, CHS hospitals have lower AMI, CHF, Stroke, and Pneumonia mortality rates than hospitals in other system types. The PSI models did not indicate any systems\u27 effects on adverse event rates. It was also found that system hospitals\u27 compliance with the JCAHO performance area indicator for availability of patient specific information was associated with lower rates of CHF, Stroke, Pneumonia, and Infection due to medical care.The findings suggest that centralization of hospital structures may improve internal clinical processes by enhancing coordination of activities, communication between providers, timely adjustments of processes of care delivery and structures to external pressures. A lack of systems\u27 effect on adverse events may be explained by a newness of the patient safety issues for hospitals and possible changes in reporting patterns of medical errors after the Institute of Medicine report of 1999. A system hospitals\u27 compliance with the JCAHO performance area indicator may indicate improvements in information and clinical record systems.Hospital systems hold much potential for hospitals in improving patient quality of care and safety because they provide a laboratory for studying the health care process and sharing lessons across multiple institutions. Based on our findings, we recommend that future studies use a combination of IQIs and PSIs when examining institutional quality of care because both provide different and complementary information