Vaccination has been perhaps the most important achievement in medicine of the last century. A hoard of infectious diseases that used to claim the lives of many, especially children, have been prevented and some even eradicated. However, it is possible that within this gift there is hidden a 'Trojan Horse'. During the last decade increasing numbers of reports regarding possible autoimmune side effects of vaccination, have been published. The existing data does not link the vaccines and the autoimmune phenomena observed in a causal relationship, nevertheless a temporal connection has been described. In this article we wish to address in particular the possible link between vaccines and systemic lupus erythematosus (SLE), namely two aspects of this inter-relationship: the occurrence of SLE following vaccination and outcome of immunization of known SLE patients.