Recent evidence from animal studies has raised the possibility that immunisation by vaccines can influence the pathogenesis of type I (insulin-dependent) diabetes mellitus. In non-obese diabetic mice and biobreeding rats, complete Freund's adjuvant and bacillus Calmette-Guérin (BCG) vaccine have successfully been used to interrupt the development of diabetes mellitus. This effect is probably mediated by nonspecific suppression of the autoimmune process. A number of attempts have also been made to assess the impact of parenteral immunisation on type 1 diabetes mellitus in humans. Epidemiological evidence has not indicated any clear link between BCG vaccination and the development of diabetes mellitus in humans. Some reports have suggested that natural mumps or mumps vaccinations can induce islet cell autoimmunity, but there is no evidence that mumps-measles-rubella mass vaccination programmes have changed the incidence of diabetes mellitus in any population. An independent protective role of measles virus has been suggested in one study. Recent studies have indicated that enterovirus infections may induce beta cell autoimmunity and clinical diabetes. The only currently available enterovirus vaccine is the poliovirus vaccine which, in theory, could modulate the protection against other enteroviruses by inducing cross-reactive T cell immune responses; however, this hypothesis has not been tested so far. In conclusion, there is no clear evidence that any currently used vaccine can prevent or induce diabetes in humans. However, only a few studies are available on the subject and therefore the possibility of a link between vaccination and diabetes mellitus cannot be excluded.