Tick-borne encephalitis virus (TBEV) is a common cause of viral encephalitis in parts of Central and Eastern Europe. Active immunization results in a high rate of seroconversion and is the most effective measure of decreasing the incidence of tick-borne encephalitis (TBE). Currently, booster vaccinations are recommended every 3 years after completion of primary immunization. However, titers of neutralizing antibodies decline with time after vaccination and with age and thus may be insufficient to protect from disease in the elderly. We report on a 54-year-old patient who had received his last booster vaccination 3 years before developing a severe TBE with delayed induction and longterm persistence of anti-TBEV-IgM-antibodies.