HCV infection is a serious concern among people who inject drugs. Despite imposing a major disease burden in countries with high rates of injection drug use such as Kazakhstan, other Central Asian and East Asian countries, Eastern Europe, and Russia, HCV remains an understudied issue. This study includes 728 individuals (364 couples) from Almaty, Kazakhstan, where at least one member of the dyad reported recent injection drug use. Participants were recruited to participate in a couple-based HIV prevention study. We examine the prevalence of HCV and co-infections between HCV and HIV, correlates of HCV, and the association between HCV prevalence and sexual behaviors after adjusting for non-injection illicit drug use, unsafe injection behaviors, and socio-demographic characteristics. Of the total sample, 90.2% of people who had ever injected drugs were diagnosed HCV positive and 15.5% of those who did not report injecting drugs were HCV positive. The prevalence of HIV and HCV co-infection among the total sample was 20.7%. In the multivariate analysis, having sex while high on alcohol and/or drugs was associated with HCV after adjusting for unsafe injection practices, non-injection drug use, and socio-demographic characteristics (PR=1.20; 95% CI=1.04, 1.39). The high rates of HCV and co-infection of HIV and HCV found in the study underscore the need for attention to HCV testing and treatment among people who inject drugs in Kazakhstan and their sex partners. Keywords: HCV, Injection drug use, Central Asia, HIV, Kazakhstan.