In western world, infectious diseases in childhood have dramatically decreased in recent years. The first reason is related to the better socio-economic conditions but the highly efficiency of immunizations programs cannot be forgotten. Nevertheless children can be still exposed to infections, as vaccines are not able to completely protect all treated patients. Anesthesiologists should be aware of the basic mechanism of immunization as it is well known that anesthesia and surgery themselves reduce human immune response. In fact, nitrous oxide depresses bone marrow function, while halothane, nitrous oxide again and isoflurane reduce neutrophil biocidal activity. On the contrary, all the anesthesia techniques (peripheral anesthesia) which inhibit stress responses have beneficial effect on the immune system function. Not urgent procedures requiring anesthesia should be deferred for three weeks after vaccination when all the related symptoms will be over. Also important is the knowledge of the incubation period that is the time from contact with a person affected by the infectious illness until the onset of the typical disease. During these periods elective anesthesia must not be performed. On the other hand, if anesthesia is delivered, the patient's ability to react can be compromised and it is possible to have florid disease exacerbation including related complications.