OBJECTIVE To determine the proportion of major surgical procedures that involve patients having serologic evidence of infection with human immunodeficiency virus-1 (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) in a single center in Westchester County, New York. METHODS Blood samples sent for transfusion screening or cross-match were tested blindly for HIV antibody (anti-HIV), HBV core antibody, HBV surface antigen (HBsAg), and HCV antibody (anti-HCV). Demographic characteristics and operation category were correlated with serologic results by univariate and regression analyses. RESULTS Of 1,062 operations evaluated, 71 (6.7%, 95% confidence interval [CI95], 5.2% to 8.4%) were performed on patients with either anti-HIV, HBsAg, or anti-HCV. In 17 (1.6%, CI95, .93% to 2.5%) of these operations, the patient evidenced anti-HIV; in 15 (1.4%; CI95, .79% to 2.3%), HBsAg; and in 55 (5.2%, CI95, 3.9% to 6.7%), anti-HCV. Anti-HCV was detected significantly more often than anti-HIV (5.2% versus 1.6%, P < .001) or HBsAg (5.2% versus 1.4%, P < .001). Operations involving women aged 25 to 44 years had the highest proportion with serologic evidence of at least one of the three viruses (17.2%); of anti-HCV (15.3%); and of anti-HIV (6.7%). Logistic regression analysis found that being in the 25- to 44-year age group was associated significantly with infection with any virus (P < .001) and with anti-HCV (P < .001). The strongest logistic predictors of anti-HIV seropositivity were having anti-HCV seropositivity (P < .001), being age 25 to 44 years (P < .001), and having a general surgery operation (P = .002). CONCLUSIONS The prevalences of serologic evidence of at least one of the three viruses (16.7%), of anti-HCV (14.5%), and of anti-HIV (5.6%) are high in patients aged 25 to 44 years undergoing major surgery at a tertiary-care medical center located in Westchester County, New York. Anti-HCV is more prevalent than anti-HIV or HBsAg and is predictive of anti-HIV seropositivity. Testing for anti-HIV alone would have detected only 24% of patients infected with a bloodborne pathogen. These data strongly underscore the importance of universal precautions.