This study determined the prevalence of human immunodeficiency virus (HIV) infection and its associated factors in female sex workers (FSWs) from the municipality of Bragança in the state of Pará, Brazil. A cross-sectional study using a respondent-driven sampling method was used to investigate 137 FSWs. They were interviewed using a questionnaire for the collection of data on their characteristics and risk behavior. Blood samples were collected for serological and molecular testing for HIV. Poisson regression models were used to estimate the reasons of prevalence (RP). The majority was single, young, poorly educated, had a low monthly income, and had worked in the sex trade for more than 7 years. Sexual services were offered either directly (easy identification of FSWs in street markets, town squares, street corners, bars, and gas stations) or indirectly/discretely (more complex identification of FSWs, offering services through a cryptic approach or an intermediary). Overall, 22 (16.06%) FSWs had anti-HIV-1/2 antibodies, and 21 (15.33%) also had complementary DNA-HIV. The use of illicit drugs [adjusted RP (aRP) = 3.13; 95% confidence interval (CI) = 1.27-8.41], unprotected sex (aRP = 4.09; 95% CI = 1.34-11.62), anal sex (aRP = 4.01; 95% CI = 1.37-10.15), the exemption of condoms for clients paying extra (aRP = 4.71; 95% CI = 1.52-10.89), more than 7 years working as a sex worker (aRP = 6.04; 95% CI = 1.20-16.33), low levels of education (aRP = 3.55; 95% CI = 1.15-11.02), and a lack of regular medical or gynecological examinations were all associated with HIV infection (aRP = 5.87; 95% CI = 1.26-15.71). The FSWs who offered their services indirectly suffered significantly less physical and sexual aggression, charged more for encounters, had a significantly higher monthly income, and were more likely to have undergone a medical or gynecological examination within the preceding 12 months. This study identified information relevant to the control and prevention of HIV in FSWs.