Vaccinations protect to a high degree against infectious diseases, but may cause side effects. In the Netherlands since 1962 the adverse events following immunizations are registered and analysed by the National Institute of Health and Environment (RIVM). Since 1983 a permanent Committee of the Dutch Health Council reviews adverse events reported to the RIVM. With the so-called killed vaccines the side effects are mainly local (redness, swelling, pain) or general (fever, listlessness, irritability, sleep and eating problems). They are seen mainly after DPT-IPV vaccination against diphtheria, pertussis, tetanus and poliomyelitis. Some side effects occur rarely (collapse reactions, discoloured legs, persistent screaming and convulsions) and very rarely serious neurological events are reported. After MMR vaccination against measles, mumps and rubella, cases of arthritis, thrombocytopenia and ataxia are reported sporadically. Usually, they have a spontaneous recovery. During recent years a scala of diseases or symptoms have been associated with vaccination (presumed side effects). Careful and extensive investigations have shown that such hypotheses could not be supported. Examples are allergic diseases as asthma, diabetes mellitus, multiple sclerosis (after hepatitis B vaccination), autism and inflammatory bowel disease (after MMR vaccination) and sudden infant death syndrome. The total number of cases where at least a possible relation between side effects and vaccination is observed--apart from local reactions and moderate general symptoms--is very rare (about 0.25 per 1000 vaccinations) and does not balance the benefits from vaccination. There appears increasing doubt about the use and safety of vaccinations. More research is needed about the motives of people to choose for and against vaccination. The education about vaccination for parents and professionals who are involved with vaccination has to be improved. Internet can play an important role.