Surgical wound infections are the most common hospital-acquired infections among patients who undergo inpatient surgery. Risk of infection is a function of both patient susceptibility and exposure. The authors studied all discharges in Pennsylvania from October 1, 2004, through September 30, 2005, in which a circulatory (n= 65 940), neurological (n= 6706), or orthopedic (n = 107 825) procedure was performed using data from the Pennsylvania Health Care Cost Containment Council. They estimated the impact of patient-specific factors on risk of infection and compared the ability of these factors to predict infections relative to hospital effects. Results suggested that for all 3 types of procedures, patient-specific factors were a significant determinant of risk of surgical wound infection. However, prediction of infection was improved by 23% to 33% when hospital fixed effects were included. Although patient-specific factors had a statistically significant association with risk of infections, much of the risk of surgical wound infections is determined by hospital factors.