Infections in disease- and/or chemotherapy-related neutropenia are major, often emergency-type problems in the treatment of pediatric oncology patients and explain the ongoing discussion about antiinfectious prophylaxis. The different aspects of prophylaxis and an overview on the literature are presented. Antiinfectious prophylaxis in pediatric oncology includes the following issues: 1. General aspects such as information for patients and parents on neutropenia and risk of infectious diseases and indication and management of reverse isolation and barrier isolation; 2. antibacterial prophylaxis with oral non-absorbable and oral absorbable antibiotics; 3. Pneumocystis carinii (Pc) prophylaxis; 4. antifungal prophylaxis to prevent disseminated candidiasis and aspergillosis; 5. antiviral prophylaxis, especially varicella-zoster-virus (VZV) post-exposure prophylaxis and cytomegalovirus (CMV) prophylaxis; 6. immunoglobulins and hematopoietic growth-factors (HGF); 7. active immunization. An evaluation of those measures leads to the following conclusions: A major controversy exists regarding antibacterial and antifungal prophylaxis. Probably not effective are the use of reverse isolation and of oral, non-absorbable antibiotics. Oral absorbable antibiotics, antifungal prophylaxis using fluconazole and amphotericin B and the use of hematopoietic growth factors are likely to be effective. Clearly effective are strict hand-washing procedures, Pc and CMV prophylaxis and passive vaccination against VZV in case of VZV exposure of a seronegative patient.