We undertook this study to determine the incidence of nosocomial surgical-site infections, apply the National Nosocomial Infections Surveillance (NNIS) index, and describe the clinical and biochemical characteristics of patients prior to a first-time ventriculoperitoneal shunt (VPS). We conducted a cohort study for 1 year with patients aged 18 years or older who underwent VPS. Patients were followed up for 30 days to identify the presence of an infection. Infection diagnosis was made according to the criteria established by the Centers for Disease Control (Atlanta, GA). A questionnaire was developed to obtain the data regarding the factors contained in the NNIS and the clinical and biochemical characteristics prior to surgery. The annual incidence of nosocomial surgical-site infections was 12.3% (9/73). Distribution of factors according to the NNIS index was as follows: 55% without any factor, 38% with one factor, 7% with two factors, and no patients with three factors. ASA RR = 2.0, 95% CI 0.4-11.4, wound type RR = 5.1, 95% CI 0.5-48.9 and surgical time RR = 0.6, 95% CI 0.1-4.2. No differences were found in the frequency of concomitant diseases. Even though the clinical and biochemical characteristics of patients who underwent first-time VPS were normal and no associated NNIS factors were identified, 12.3% of the patients developed a nosocomial surgical-site infection. These results suggest the existence of factors other than those contained in the NNIS, which are possibly extrinsic to the individual and may influence the development of infections.