To estimate HIV-1 seroprevalence in the general population of Salvador, Bahia, Brazil, we conducted a cross-sectional survey of 3,437 residents from 1998 to 2000. Subjects were drawn from 30 sentinel areas representing a wide range of living conditions. Plasma samples were screened for HIV-1 antibodies by ELISA and confirmed by immunofluorescent assay. Subtype determination by HMA was performed after proviral DNA amplification. Phylogenetic analysis using parsimony was performed with the neighbor-joining method. Overall HIV-1 seroprevalence was 0.55% (19/3,446): 0.8% for men and 0.36% for women. Seroprevalence was higher in the 31-45-year age group (1%) and among persons with family income less than twice the minimum wage (0.78%) as compared to 0.33% for the higher income group. Syphilis was detected in 37% of HIV seropositive individuals. Phylogenetic inferences identified 10 samples as subtype B in the env region and 2 samples with Benv/Fgag/Fpol and Fenv/Bgag. Age > or = 30 years, male gender, and income < or = 2 times the minimum wage were identified as risk factors for HIV-1 infection. Extrapolating the proportion of seropositive individuals to Salvador, the number of HIV-1 infected individuals was estimated at 13,750.