Although Brazilian spotted fever is known to occur in several adjacent states, infection with spotted fever group (SFG) rickettsiae has not previously been documented in the Brazilian state of Espirito Santo. We report a cluster of two proven and four suspected cases of Brazilian spotted fever in a small valley near Colatina, Espirito Santo. Four patients died without confirmatory serologic or pathologic studies. The two surviving patients had serologic and/or pathologic evidence of infection with SFG rickettsiae. Results of a survey done in 1991 confirmed the presence of antibodies reactive with SFG rickettsiae in the serum of dogs living in this region. Two of 25 dogs had elevated microimmunofluorescent antibody titers (1:64 and 1:256). Both seropositive dogs were pets of the index cases and lived in the valley where all six human cases were presumed to have acquired their infections. These cases and the results of the canine serosurvey suggest that a focus of virulent disease exists in an area not previously known to be endemic for SFG rickettsiae.