The prevalence and incidence of antibodies to Orientia tsutsugamushi, the etiologic agent of scrub typhus, in Thai soldiers living and working near the Thai-Cambodian border in Si Sa Ket Province was investigated. The point prevalence of antibodies varied from 0 to 4.1%. The incidence of antibodies, calculated from individuals who seroconverted following a negative result in a previous bleeding 3 to 5 months earlier, was 4.21% (9/214) in January 1992, 0 in April 1992 and 3.76% (8/213) in September 1992. An annual infection rate of 2.66% was estimated.