The clinical impact of surgical site infections (SSI) and postoperative pneumonia (PP) after head and neck cancer surgery has been assessed in the past, but little is known about their economic impact. The present study was designed to evaluate costs related to SSI and PP after head and neck cancer surgery with opening of mucosa. The incidence of SSI and PP was measured in a prospective cohort of 261 patients who had undergone head and neck cancer surgery. The additional direct medical costs related to these infections from the hospital perspective were determined based on postoperative length of stay. The mean direct hospital costs for patients with and without SSI or PP were compared. Of the 261 patients, 81 (31%), 21 (8%) and 13 (5%) developed SSI, PP or both, respectively. The additional lengths of stay attributable to SSI, PP or both were 16, 17 and 31 days, respectively, and additional direct medical costs related to these conditions were 17,000, 19,000 and 35,000 Euros. Nosocomial infections after head and neck cancer surgery significantly increase patients' length of stay and therefore generate additional direct medical costs. These results support the application of preventive interventions to reduce nosocomial infections in this setting.