Immunocompromised patients in pediatric hematology-oncology are faced with an increased risk of nosocomial infections (NI). The incidence of NI and the contribution of certain risk factors have not sufficiently been investigated in this population. It is therefore unknown how many NI are preventable through infection control measures. The surveillance of NI in pediatric hematology-oncology departments should focus on device-associated infections (central venous catheter infection, urinary tract infection), on nosocomial pneumonia (in particular due to Aspergillus) and on infectious complications caused by Respiratory Syncytial-Virus and Rotavirus. The surveillance protocol should be based on a modified version of the Centers for Disease Control and Prevention methods (established definitions of NI can not be completely applied to pediatric oncology patients). Prospective surveillance for NI on pediatric hematology/oncology units is an indispensable tool for internal quality control. The careful evaluation of specific NI-rates permits the identification of critical control points, that may be targeted by infection control programs.