Over a 5 month period, a study of the incidence of nosocomial infections (NI) was carried out in the Léon Bérard Oncology Center (Lyons). It comprised 1,551 patients classified in groups according to the site of origin of the underlying malignancy. The respective frequency of the different types of nosocomial infections and the responsible agents was evaluated in each group and the incidence was calculated per day of hospitalization. The overall incidence of NI was 11.29 per 1,000 patient-days, with a maximal value of 20.04 for patients suffering from lymphomas. The most frequently encountered infections were bacteremias (22.7%), followed by urinary tract infections (20.8%) and wound infections (20.5%). The most frequent causative agents of NI were Escherichia coli (25.8%), Pseudomonas aeruginosa (13.9%), Staphylococcus aureus (9.8%) and Staphylococcus epidermidis (9.8%). The latter micro-organism together with Escherichia coli were the most frequent causative agents of bacteremias. Even though cancer patients are particularly prone to developing infections, the incidence of NI could be reduced thanks to a program of control and surveillance of infectious episodes during hospitalization.