OBJECTIVES: The aim of this study was to evaluate the impact of race on quality of anticoagulation control in patients undergoing major orthopedic surgery. METHODS: We conducted a retrospective, observational cohort study in an inner-city underserved population treated with warfarin thromboprophylaxis after total hip replacement (THR) or total knee replacement (TKR), referred to a specialized antithrombosis clinic from 1998 to 2009. Significant variables from simple linear regression (p <0.1) were entered in stepwise multivariate logistic regression (alpha <0.05) to evaluate the effect of race on quality of anticoagulation control, defined as within-patient proportion of international normalized ratio (INR) levels spent in therapeutic range (INR of 2-3 ± 0.2).  RESULTS:   A total of 400 consecutive patients were evaluated. The average age was 58.4±12.5, 56% were African-American, and 26% were Hispanic. The average length of warfarin therapy was 50±21 days, and the average within-patient proportion of INR levels spent in therapeutic range was 39.2±20.5%. African-Americans (β= -8.59, p <0.0001) had lower within-patient proportion of INR levels spent in therapeutic range compared to non-African-Americans. In addition, males (β= -5.17, p = 0.0069), higher warfarin dose (β= -3.13, p <0.0001), higher frequency of anticoagulation monitoring visits (β= -1.13, p = 0.0214) and non-adherence with warfarin (β= -0.31, p <0.0001) were significantly associated with a lower proportion of INR levels in therapeutic range. After controlling for age, gender, comorbidities, and significant covariates, the effect of African-American race remained significant (β= -6.90, p = 0.0001). CONCLUSIONS: In this inner-city underserved population treated with warfarin thromboprophylaxis for THR and TKR, African-Americans tended to have lower proportion of INR levels in therapeutic range than non-African-Americans. Studies are needed to further elucidate factors driving substandard anticoagulation control in minority patients.