The present study has been carried out to estimate the prevalence of HCV among HIV-positive individuals in the state of Mato Grosso, Central Brazil, as well as to identify the associated epidemiological factors. One thousand and eight individuals over 18 years of age bearing HIV/aids and being attended in the reference public health network of the state of Mato Grosso participated in this research. HIV-positive subjects were interviewed and blood samples were taken to be tested for anti-HCV antibodies by enzyme immunoassay (EIA). The anti-HCV antibodies were investigated in all the individuals by immunoenzymatic assay. The reactive samples in duplicate were submitted to a polymerase chain reaction (PCR) to detect HCV-RNA. The positive tests were submitted for genotyping by the LIA method. One hundred and ten (10.9%; CI 95%: 9.1-13.0) HIV-positive individuals presented anti-HCV by EIA. The PCR was positive in 60 (6.0%; CI 95%: 4.6-7.6) individuals. The 1a genotype was the most frequent, followed by the 3a and 1b. The genotype 2 was found in only one individual. There were more male and intravenous drug users among HIV-HCV coinfected individuals when compared to only HIV-infected individuals. Multivariate analysis revealed an association between the HIV-HCV coinfection, regarding either EIA or PCR results, and the use of intravenous drugs, the presence of tattoos, and having received blood transfusions before 1994. There was no association of the coinfection with the variables related to sexual transmission. The relatively low prevalence of HCV infection in the HIV-positive population in that region may be a consequence of a small number of intravenous drug users in the sample, despite a strong association between HCV infection and use of intravenous drugs.