Health care-associated infections (HAIs) occur frequently in hospitals and have severe consequences, with surgical site infection (SSI) being one of the most commonly reported. The aim of this study was to determine SSI rates and to asses the application of presurgical preparation and antimicrobial prophylaxis protocols in 14 public hospitals of the region of Madrid. Multi-centre prospective surveillance study. All patients who underwent a surgical procedure from January 1 2009, to December 31, 2009 with a hospital stay of more than 48 hours, were monitored from the time of surgery until hospital discharge. SSI was the most frequent HAI (superficial incisional SSI=1.7%; deep incisional SSI=2%; organ-space SSI=1.7%). SSI rates are provided by operative procedure and NNIS risk index category. Further quality indicators reported are surgical complications, length of stay, antimicrobial prophylaxis, mortality, readmission due to infection or other complications and revision surgery. The results obtained in this multicentre study can be used as a reference for other public hospitals, and allow comparisons with other international surveillance systems. Surveillance and control of HAIs must be a key aspect in patient safety and quality healthcare programs.