Background: Hepatitis C virus (HCV) is a major global problem, transmitted primarily by percutaneous exposure to contaminated blood. Goal: The goal of the study was to determine the seroprevalence of and risk factors for HCV among patients attending two urban STD clinics in Alberta. Study Design: Anonymous unlinked serosurveys were performed with use of leftover sera. Self-administered questionnaires collected information on demographics, sexual behaviors, and drug use. Results: The seroprevalence of HCV was 3.4% (209 of 6668 patients). Univariate analysis revealed that infection was higher among nontherapeutic needle users (RR = 80.9), those coinfected with HIV (RR = 8.09), individuals over the age of 20 years (RR = 6.68), those of aboriginal ethnicity (RR = 5.54), those with a history of STD (RR = 3.43), men (RR = 2.2), and bisexuals (RR = 2.23). Not utilizing condoms and engaging in prostitution or exchanging money or drugs for sex were also risk factors. In multivariate analysis, nontherapeutic needle use remained highly significant (RR = 60.54-65.51). Other significant factors included sex, age, ethnicity, a history of STD, and HIV infection (RR = 1.72, 4.62, 3.18,1.69, and 2.56, respectively). Sexual orientation and sexual practices were not significant without a history of drug use. Conclusion: Nontherapeutic needle use is the strongest predictor of HCV infection.