Risk stratification has proven to be a useful tool in surgical site infection prevention. The duration of the surgical procedure has been recommended for use in surgical site infection (SSI) risk stratification (Infect Control Hosp Epidemiol 20:247-248, 1999). A retrospective analysis of 6489 patients who underwent total knee replacement (TKR) between 1993 and 1999 assessed the association between the duration of the surgical procedure and the risk of postoperative infection. One hundred thirteen infected patients were matched with 236 controls, and nominal variables were statistically processed. Patients without infections (n = 236) had surgery durations of 94 +/- 28 min, and patients with infection (n = 104) had durations of 127 +/- 45 min (p < 0.001). Operation time has positive correlations with weight (r = 0.3, p < 0.001), body mass index (r = 0.3, p < 0.001), and the total number of comorbidities (r = 0.2, p < 0.001; n = 340). The results confirm that the duration of the surgical procedure can be used as a risk predictor for SSI in TKR.