Immunization against infectious diseases is one of the most effective and economical way to protect individual and the entire population of certain infectious diseases. In the body of immunized person it creates specific antibodies which protect body of certain infectious diseases. Immunization can be long-term or short-term depending on whether it is active or passive. In the Republic of Croatia vaccination against certain infectious diseases is required by law. In the last few years, appears a trend of parents refuse to immunize their children because of statements that vaccination had a terrible side-effects on health of treated children. The easiest and fastest source of information is of course the Internet. The Internet is also a place where everyone can write what he wants and also published without many verifying authenticity. Leaded by many unsubstantiated statements, parents started to gather them in social network groups, forums, etc. where they can share different experiences regarding vaccination, advices if vaccination is needed at all. The number of groups is increasing each day so parents get confused not knowing what or who to believe. The incidence of side effects after vaccination is important as vaccination, because, without them, we could not react on time and continue with testing vaccine. Noticing the problem of lack of information and increase resistance to vaccination, the decision was made to make a questionnaire which obtains information about vaccination of children, sources of informing and the factors that influence the final decision of parents about vaccination. According to the survey it can be concluded that the general awareness of vaccination is insufficient. Therefore, in addition to care and help with the sick, the task of health care workers is good communication with them or with their families. Health care workers should point out to parents the need for information and help them understand the risks and overcome fears of vaccination itself.