Since the early 1990s, the five coordination centers for the control of nosocomial infections (C.CLIN) have established interregional surveillance networks for surgical site infections (SSI) involving volunteer surgical departments. Common surveillance methods for the five C.CLINs were defined in 1999, and since 2001 these networks have been coordinated within the Network for Alert, Investigation, and Surveillance of Nosocomial Infections. Each year, participating departments conduct a three-month incidence survey. Individual patient risk factors and procedure characteristics are documented at the time of the procedure, and patients are followed up for up to 30 days afterward. In 1999 and 2000, 162,151 procedures were included; 3,129 (1.93%, 95% CI = [1.86%–2.00%]) procedures were followed by a surgical site infection (SSI). Among these infections, 1,269 (41%) were deep incision infections or infections of the operated organ, site, or space. The incidence of SSI varied according to the procedure’s infection risk (measured by the NNIS score), ranging from 1% for procedures classified as NNIS 0 to 16% for procedures classified as NNIS 3. These surveillance data will help guide national policy on combating these infections. (R.A.)