Over 500million people live in yellow fever (YF) endemic areas and more than 3million travel to endemic countries every year. Prevention against YF, caused by the YF virus, an arbovirus, can only be efficiently obtained by active immunization. The vaccine is well tolerated and severe adverse events are very rare. Exceptionally, YF vaccination may result in serious adverse events, such as viscerotropic and neurotropic diseases, sometimes with a fatal outcome. These rare serious adverse advents are reviewed with their potential risk factors, such as advanced age or history of thymus disease. The benefit/risk ratio remains in favour of vaccination, although the decision to offer yellow fever vaccination, especially to persons 60years of age or older, should be evaluated according to the planned trip. Additional research investigations should be made on the host immune response since this response is considered to be at the origin of these severe adverse events.