Vaccination against tick-borne encephalitis with FSME-Immun® vaccine was started in the Department of Infectious Diseases, University Medical School of Białystok, Poland, in 1992. No serious adverse reactions after vaccine administration were observed. Post-vaccine side effects were reported in 242 (11.3%) persons after the first dose (n=2,135) and only in 14 patients (1.2%) after the second one (n=1,183). These effects were mild and transitory. No relationship was observed between the frequency of adverse reactions, general or local, and the initial anti-TBE virus antibody titres or the age of the immunized individuals. Post-vaccine side effects were reported significantly more frequently among people not bitten by ticks.