We studied the role of sexual transmission in the epidemiology of HCV by a cross-sectional study comparing prostitutes and HCV seropositive and seronegative sexual clients recruited from the bordellos of the docks of Santos, São Paulo State. The average age in the prostitute group was 27.2 years. The median time spent in prostitution was 3 years. The average number of clients per week was 7. A total of 5.2% of the prostitutes admitted to having used injectable drugs. Nine percent patients said that they had received a blood transfusion and 36.3% claimed to have had a sexually transmissible disease in the past. The prevalence of HCV antibodies was 10.9%. There was a positive and independent relationship between HCV seropositivity and the following variables: use of injectable drugs (OR = 5.2; 95% CI = 2.2 to 12.2), prior blood transfusion (OR = 2.3; 95% CI = 1.08 to 4.9), time spent in prostitution (OR = 2.0; 95% CI = 1.13 to 3.6), and a positive FTA-ABS result (OR = 1.7; 95% CI = 0.95 to 3.0). The risk factors indicating parenteral exposure (use of an injectable drug and prior blood transfusion) presented a stronger relationship with HCV seropositivity. The time spent in prostitution and FTA-ABS positivity, risk factors indicating sexual exposure, also presented a positive relationship with HCV seropositivity, suggesting a significant role for sexual transmission in HCV epidemiology, particularly in groups involved in promiscuous sexual behavior.