Background/aim: Besides infections of urinary tract and pneumonias, as well as blood infections, surgical site infections (SSI) represent one of the most common localization of hospital infections. The aim of this study was to determine the incidence of SSI in the departments of orthopedics and traumatology as well as the SSI incidence in relation to the ASA score, surgical site contamination class and NNIS index. Methods. A prospective cohort study followed daily all the surgical patients hospitalized over 48 hours in the Institute for Orthopedic Surgery and Traumatology, Clinical Center of Serbia, as well as 30 days after the discharge, during the period between February 1 to July 31, 2002. The patients were examined and their diagnoses made according to the definition of hospital infections, i.e. upon clinical and/or laboratory analyses, using concurrently the ASA score, surgical site contamination class and NNIS index. Results. Out of 227 surgical patients, 60 were diagnosed with SSI during their hospitalization, while 3 of the patients developed SSI after the discharge. The incidence of SSI was 22.7% (95% CI = 17.8−27.6). In the patients with good health condition, i.e. ASA ≤ 2, the incidence of SSI was 18.3% (43/235) and in those with ASA > 2, it was 47.6% (20/42) (χ2 = 17.4; p < 0.001). The incidence of SSI was 13.5% (25/185) in the clean wounds, 11.6% (5/43) in purely contaminated, while it was much higher in the contaminated 65.5%; (19/29) and soiled 70.0%; (14/20) wounds (χ2 = 67.6; p < 0.001). The incidence of SSI in relation to NNIS was 8.1% (13/161) in the patients with score 0, then 36.4% (32/88) in the patients with score 1, and 64.3% (18/28) in the patients with the scores 2 and 3 (χ2 = 57.3; p < 0.001). The patients with SSI stayed in the departments of orthopedics and traumatology approximately 1.8 times longer than the patients without SSI (t = 5.3; DF = 275; p < 0.0019. Conclusion. It is important to emphasize the need for constant epidemiological surveillance of SSI and the implementation of preventive measures in Serbia.