Introduction. The surveillance on adverse reaction following immunization was aimed at recording all adverse events possibly related with vaccines. During the implementation of immunization strategy against pandemic influenza A(H1N1) in 2009, the post-marketing comprehensive surveillance was suggested to be conducted due to limited clinical experience in applying this particular vaccine and because of the fact that some vaccines had been licensed only on the basis of the data regarding their quality. Material and Methods. The passive surveillance on adverse events following immunization was conducted simultaneously with immunization campaign against pandemic influenza in the Autonomous Province of Vojvodina. Reporting of adverse events was conducted by health care service through a specially designed questionnaire Results. In the period from December 17th 2009 to February 7th 2010, of the total number of 55720 people who were vaccinated, 50433 received one dose and 5287 received two doses of vaccine. The total number of doses administered was 61007. During the observed period, some adverse reactions were recorded in 37 people, the rate of occurrence of adverse reactions being 6.6 per 10.000 vaccinated. Since the majority of patients had several symptoms and signs, the number of recorded clinical manifestations was much higher (140) than the number of patients with reactions. The dominant symptoms and signs were fever (51.4%), weakness/fatigue (48.6%), headache (40.5%) and myalgia (31.5%). The reactions in the majority of patients were mild and transient. Only two patients sought medical care and one was hospitalized. Since the immunization coverage was very small, it was not possible to record rare adverse events, whose expected incidence is, anyway, very low. Conclusion. Surveillance on adverse reaction following immunization represents an important component of immunization program, especially when new vaccines are introduced. Therefore, this form of surveillance in our country needs further improvement in order to provide more complete information on occurrence and characteristics of adverse reactions following immunization.