To estimate the prevalence and identify factors associated with hepatitis C virus (HCV) infection among men and women in Karachi, Pakistan. We conducted a cross-sectional study of adult men and women in a peri-urban community of Karachi (Jam Kandah). Households were selected through systematic sampling from within all villages in the study area. All available adults within each household were interviewed about potential HCV risk factors. A blood specimen was collected to test for anti-HCV antibodies by enzyme immunoassay. We used generalized estimating equations while accounting for correlation of responses within villages to identify the factors associated with HCV infection. Of 1997 participants, 476 (23.8%) were anti-HCV positive. Overall, HCV infection was significantly associated with increasing age, ethnicity, and having received > or =2 blood transfusions, > or =3 hospitalizations, dental treatment and >5 injections among women. Among women, > or =2 blood transfusions [adjusted odds ratio (aOR) = 2.32], >5 injections during the past 6 months (aORs = 1.47), dental treatment (aOR = 1.31) and increasing age(aOR = 1.49), while among men, extramarital sexual intercourse (aOR = 2.77), at least once a week shave from barber (aOR = 5.04), > or =3 hospitalizations (aOR = 2.50) and increasing age (aOR = 1.28) were associated with HCV infection. A very high prevalence of HCV was found in the study population. Among women, unsafe health care practices, while among men extramarital sex, shaving from a barber and hospitalizations were associated with HCV infection. Efforts are needed to improve the safety of medical procedures to reduce the transmission of HCV in Pakistan [Corrections made in Summary after initial online publication.].