According to the National Nosocomial Infection Surveillance system we analysed the post-surgical nosocomial infections in a surgery ward of Perugia University. Between May 2000 and April 2001, 677 patients were enrolled mean age 51.5 years: 355 (52%) male, 462 (68%) ASA score 1, "clean" surgery in 355 cases (52%), cephazolin prophylaxis in 256 (38%); 11 (2%) patients deceased perioperatively. A total of 37 nosocomial infections, in 33 patients, were detected: 18 pneumonia (48.6%), 10 surgical site infections (27%) with 18 isolated: 12 gram-negative (E. coli 3, Acinetobacter baumannii 2, Providencia stuartii 2, Pseudomonas aeruginosa 2, Achromobacter spp. 1, Citrobacter freundii 1, Morganella morgani 1) and 6 gram-positive (Staphylococcus aureus meticillin resistant 3, Enterococcus faecalis 2, Streptococcus salivarius 1); 7 sepsis (19%) due to 7 gram-positive (S. aureus meticillin resistant 4, S. aureus meticillin susceptible 1, Staphylococcus coagulase negative 1, Clostridium spp 1), 2 urinary tract infections (5.4%). Patients without infections and with nosocomial infections spent in hospital 6.3 and 16.6 days respectively. We can image that in one year 53 surgical procedure were lost, with a lost gain of 79.500-291.500 euro/year.