Vaccination has been an important part of antiinfectious prophylaxis in pediatric oncology comprising immunizations with special indication like varicella vaccine and follow-up of routine immunizations after chemotherapy and bone marrow transplantation (BMT). Studies from the last decade demonstrate a loss of long term immunity to immunization preventable disease in most patients with chemotherapy and BMT who had received appropriate immunization before. So far routine vaccination programs following intensive chemotherapy have not been studied prospectively. Immunization programs following BMT have shown that immunizations with tetanus toxoid, diphtheria toxoid, inactivated poliovirus vaccine and influenza vaccine - given at least 12 months after transplantation - are safe and effective. Vaccination with live attenuated trivalent vaccine against measles, mumps and rubella in patients without chronic "graft versus host disease" (GVHD) and without ongoing immunosuppressive therapy, performed 24 months after transplantation, proved to be safe too. Recommendations have been published by 5 different official groups: (1.) "Ständige Impfkommission" (STIKO) and (2.) "Deutsche Gesellschaft für pädiatrische Infektiologie" (DGPI) recommend varicella vaccine für children with leukemia in remission for at least 12 months, for children with solid tumors and for patients getting an organ transplantation. Both societies do not comment on the schedule of booster vaccinations (with live attenuated vaccines) after the end of chemotherapy and after BMT. (3.) "Qualitätssicherungsgruppe" der "Gesellschaft für pädiatrische Onkologie und Hämatologie" (QS-GPOH) recommends immunization with nonliving vaccines when the patient is off therapy for at least 3 months and immunization with live attenuated vaccines when he is off therapy for at least 6 months. This group does not comment on varicella vaccine which has been controversial among pediatric oncologists. (4.) The " Infectious disease working party of the European group for Blood and Marrow Transplantation" (EBMT) recommends immunization with nonliving vaccines when the patient is off transplantation for at least 12 months, without GVHD and without immunosuppressive therapy. (5.) The "Guidelines for Preventing Opportunistic Infections Among Hematopoietic Stem Cell Transplant (HSCT) Recipients" published by the following american institutions and societies: "Centers for Disease Control and Prevention", "Infectious Diseases Society of America" and "American Society of Blood and Marrow Transplantation" recommend that patients should be routinely revaccinated after transplantation if they are off immunosuppressive therapy and do not suffer from GVHD: beginning of vaccinations with nonliving vaccines in the second year after HSCT, beginning of vaccinations with live attenuated vaccines in the third year after HSCT. Life-long seasonal influenza vaccination is recommended for all HSCT candidates and recipients, beginning during the influenza season before HSCT and resuming > 6 months after HS...