Introduction: Vaccination or inoculation is the administration of live weakened, dead organisms or their toxins for the purpose of infectious disease prevention. Vaccination of children is carried out under the authority of the National institute for public health under the so called mandatory vaccination program. It is a safe and efficient system for protection of our children from severe infectious diseases. With vaccination we can prevent spreading of infectious diseases among the rest of the population who cannot be vaccinated on medical grounds. Thus we ensure the protection of the youngest age group which could suffer the worse course of disease. Vaccination is the greatest medical achievement which has reduced mortality in recent years. Purpose: The purpose of this thesis is to ascertain the parents’ opinions on mandatory vaccination program. My main focus was on parents’ general opinion on vaccination, the source of information on vaccination, the health personnel’s influence on vaccination program and parents’ reasons for rejecting the vaccination program. Methods: Quantitative research paradigm was used. To establish the research problem literature in Slovene and English language was reviewed, carried out with electronic databases such as Medline (PubMed), CINAHL, Science Direct, with Google Scholar browser and COBISS. Literature search criteria: article age, contextual relevance and full text accessibility. For the purpose of empirical research a structured questionnaire, aimed at all parents with a child aged between 3 months and 10 years was used. The questionnaire was used in electronic form on web page 1 Ka or EnKlikAnketa. The survey took place in June 2017. Results: 807 respondents, parents of children aged between 3 months and 10 years took part in the survey. Most parents receive the greatest amount of information on internet (32%), followed by paediatricians (14%), next from relatives (12%) and friends (11%). A quarter receives information from a nurse with a degree and social networks. Half of the parents claims that the health personnel failed to provide conversation time, solving dilemmas related to vaccination and 66% state that they did not receive information on possible side effects from the health personnel. A good third of the parents approve of the vaccination program and vaccinate their children according to it, whereas almost a third rejected to vaccinate their children. Vaccines against pneumococcal, hepatitis B, measles, mumps and rubella are most commonly refused. Reasons for rejection vary, however, there are two main ones: side effects of vaccines (short term/long term) and harmful substances contained in them. Half of the parents who took part in the survey state, that they would not vaccinate their child if it were not mandatory. Discussion and conclusion: More research is necessary to enable a holistic insight in the problem of vaccination rejection. It would be important to investigate from which web sites the parents who reject vaccination obtain their information. The final result of the research illustrates lack of knowledge, health education, health promotion and quality treatment on the side of health professionals.