The high standard of safety that is expected from vaccines can only be obtained if these products undergo in depth evaluation of their side effects before marketing authorization is guaranted, as well as post-marketing surveillance and investigation of reported adverse events. The evaluation of the benefit/risk balance of vaccines is a dynamic process, influenced by the residual impact of the target disease and by the existence of alternative preventive or therapeutic approaches. The efforts made to ensure the safety of vaccination must be brought to the attention of the public and the health workers to maintain confidence in this important public health intervention.