Tick-borne encephalitis (TBE) is a viral illness endemic to the Balkan region. United States military forces were deployed to Bosnia in early 1996 as part of Operation Joint Endeavor, a U.S.-led multinational peace-keeping operation. To counteract the TBE threat, an inactivated, parenteral vaccine (FSME-Immun Inject; Immuno AG, Vienna, Austria) was offered to soldiers at high risk on a volunteer basis in an accelerated, 3-dose schedule (0, 7, and 28 days). Passive adverse reaction surveillance was conducted on 3,981 vaccinated personnel. Paired sera from a randomly selected group of 1,913 deployed personnel (954 who received vaccine and 959 who were unvaccinated) were tested for antibodies to TBE by an ELISA. Three-dose recipients demonstrated an 80% seroconversion rate (4-fold or greater increase in anti-TBE titers). By comparison, the TBE infection rate in the unvaccinated cohort was found to be only 0.42% (4 of 959). Only 0.18% of vaccinees reported self-limited symptoms. An accelerated immunization schedule appears to be an acceptable option for military personnel or travelers on short-term notice to TBE-endemic areas.