BACKGROUND AND OBJECTIVES. Prostitutes are a greater risk for hepatitis B virus (HBV) infection than the general population. We studied the influence of age and time as prostitute on HBV infection. We also examined the relationship between syphilis and HBV infection in a cohort of female prostitutes. STUDY DESIGN. The presence of hepatitis B surface antigen (HBsAg), antibodies to hepatitis B core antigen (anti-HBc), antibodies to hepatitis D virus (anti-HD) and treponemal antibodies (FTA-ABS) were determined in 368 prostitutes, of whom 147 were submitted to medical and serological follow-up every six months to evaluate the influence of syphilis in the transmission of hepatitis B. RESULTS AND CONCLUSION. The prevalence of HBsAg was 4.6%, of anti-HBc 31.2%, anti-HD 0.5% and FTA-ABS 35.0%. There was a statistical association between the presence of treponemal antibodies and anti-HBc (P = 0.022). The cohort study performed shows that the accumulated incidence of HBV infection in the FTA-ABS positive prostitutes (24.6%) was significantly higher than that of the FTA-ABS negative group (9.7%) (RR = 2.544; P = 0.034). Our results indicate that syphilis could facilitate the heterosexual transmission of HBV infection.