Scrub and murine typhus have been identified as causes of illness among the 238,000 displaced Khmer people residing in temporary settlements on the Thai side of the Thai-Cambodian border. Still, the true extent of the problem and the relative frequency of infection with scrub typhus as compared to murine typhus are unknown. We evaluated consecutive patients with unexplained pyrexia (documented fever, no exclusionary diagnosis, and constitutional symptoms) in 1 temporary settlement over 1 month. Laboratory studies included culture of blood and assay of paired sera for rickettsial IgM and IgG antibody, for dengue IgM and IgG antibody, and for leptospiral IgM and IgG antibody. Among 37 patients (27 adults and 10 children), 28 (75%) had a rickettsiosis (26 cases of murine typhus and 2 cases of scrub typhus). No case of enteric fever, dengue, or leptospirosis was diagnosed. The illnesses of 9 patients were not identified. Signs and symptoms did not distinguish confirmed rickettsial infections from undiagnosed illnesses. The 1 month attack rate of rickettsial infection was 29/100,000 for children and 185/100,000 for adults. Murine typhus was a major cause of febrile illness in this settlement.