Surgical site infections (SSI) are the most-common healthcare-associated infections among surgical patients and have severe adverse consequences. Surveillance is the ongoing systematic collection,... Show moreSurgical site infections (SSI) are the most-common healthcare-associated infections among surgical patients and have severe adverse consequences. Surveillance is the ongoing systematic collection, analysis, interpretation, and feedback of data, and has been accepted worldwide as a primary step toward prevention of healthcare-associated infections. In the Netherlands, a national network for the surveillance of healthcare-associated infections was set up in 1996 and called PREZIES (__PREventie van ZIEkenhuisinfecties door Surveillance__). In this thesis, the quality of the SSI surveillance within this network is evaluated. The method for postdischarge surveillance recommended by PREZIES seemed feasible and effective, and the mandatory validation visits ensured reliability and robustness of the surveillance data. Furthermore, the predictive power of the NNIS risk index was sufficient for several surgical procedures and could not be significantly improved by using other procedure-specific determinants. Analysis of the time-trend in SSI rates for five surgical procedures showed encouraging decreasing trends, although mostly not statistically significant. Comparison of the Dutch and German SSI surveillance data revealed that even though similar infection surveillance protocols were used, differences occurred in the implementation which hampered the comparison of SSI rates. Additionally, PREZIES contributed to a multi-center intervention project to improve the quality of surgical prophylaxis. Show less