Brazilian spotted fever (BSF) is the most important tick-borne disease in Brazil and is caused by Rickettsia rickettsii and transmitted by the Ixodid tick Amblyomma cajennense, its main vector. We present epidemiologic aspects of a case series of patients admitted to the Hospital das Clinicas da UNICAMP from 1985 to 2003 with a confirmed diagnosis of BSF either by a fourfold rise in indirect immunofluorescence (IFA) titers of IgG antibodies reactive with R. rickettsii or isolation of R. rickettsii from blood or skin specimens. Seasonal variation of case occurrence seems to be associated with the life cycle of the tick. The recent reemergence of cases seems to be associated with the growing numbers of the capybara (Hydrochaeris hydrochaeris) and their expansion into urban areas. © 2006 New York Academy of Sciences.1078 170172Sangioni, L.A., Horta, M.C., Vianna, M.C., Rickettsial infection in animals and Brazilian Spotted Fever endemicity (2005) Emerg. Inf. Dis., 11, pp. 265-270Lemos, E.R.S., Alvarenga, F.B.F., Cintra, M., Spotted fever in Brazil: An epidemiological study and description of clinical cases in an endemic area in the state of São Paulo (2001) Am. J. Trop. Med. Hyg., 65, pp. 329-334Horta, M.C., Labruna, M.B., Sangioni, L.A., Prevalence of antibodies to spotted fever group rickettsiae in humans and domestic animals in a Brazilian Spotted Fever endemic area in the state of São Paulo, Brazil: Serologic evidence for infection by Rickettsia rickettsii and other Spotted Fever Group rickettsia (2004) Am. J. Trop. Med. Hyg., 71, pp. 93-97Dias, E., Martins, A.V., Spotted fever in Brazil: A summary (1939) Am. J. Trop. Med., 19, pp. 103-108Gaevão, M.A.M., Dumler, J.S., Mafra, C.L., Fatal spotted fever rickettsiosis, Minas Gerais, Brazil (2003) Emerg. Inf. Dis., 9, pp. 1402-1405Lima, V.L.C., Souza, S.S.L., Souza, C.E., Spotted fever in Campinas region, State of São Paulo, Brazil (2003) Cad. Saúde Públ., 19, pp. 331-334Thorner, A.R., Walker, D.H., Petri, W.A., Rocky Mountain spotted fever (1998) Clin. Inf. Dis., 27, pp. 1353-1360Febre Maculosa, , http://www.cve.saude.sp.gov.br/htm/Cve_fmaculosa.htm, Available at [accessed in July 30, 2005]