Studies have demonstrated that subspecialists (SUBS) provide better quality care when working within their subspecialty as compared to primary care physicians (PCPs). However, many SUBS care for patients outside of their subspecialty. There are no data demonstrating that SUBS treating patients outside of their specialty provide worse care than PCPs or SUBS practicing within their specialty. OBJECTIVES: Our purpose was to compare the quality of care provided by SUBS practicing outside of their subspecialty with PCPs and SUBS practicing within their subspecialty. METHODS: We studied 5,112 patients hospitalized with pneumonia (CAP), acute myocardial infarction (AMI), congestive heart failure (CHF), and upper gastrointestinal hemorrhage (UGIB) at 6 hospitals in Cleveland. RESULTS: There were statistically significant increases in severity-adjusted length of stay (LOS) comparing SUBS practicing outside of specialty with those practicing within specialty for patients with CHF (23% increase, 95% CI 15%,32%), UGIB (22% increase, 95% CI 7%,39%) and CAP (14% increase, 95% CI 4%,24%). Severity-adjusted mortality (MORT) was higher for all patients combined when comparing SUBS outside of specialty with those within specialty (mortality odds ratio 1.46, p<0.05). When comparing PCPs with SUBs practicing outside of specialty, LOS was longer for SUBs practicing outside of specialty for CHF (16% increase, 95% CI 8%,26%), UGIB (15% increase, 95% CI 2%,30%), CAP (18% increase, 95% CI 9%,28%). CONCLUSIONS: Our data suggest that SUBS caring for patients outside of their subspecialty may have longer LOS than SUBS practicing within specialty or PCPs, and may have higher MORT. Our findings have implications for health care systems where SUBS care for patients outside of their chosen subspecialty.