Background and aim. Resistance-associated variants (RAVs) on the NS3 region of the hepatitis C virus (HCV) may be relevant for antiviral therapy, but data in human immunodeficiency virus (HIV) coinfected patients are scarce. We assessed frequencies of NS3 RAVs in patients infected with HCV genotype 1a with or without HIV coinfection. MATERIAL AND METHODS: HCV NS3 amino acids 1-181 were sequenced by the Sanger method and analyzed for RAVs. RAVs and their distribution between HCV genotype 1a clade I and II viruses were compared between HIV-infected versus HIV-uninfected patients. RESULTS: 148 samples were available (n = 68 HIV and n = 80 non-HIV). Relative frequency of clade I and clade II was significantly different between HIV (85% and 15%) and non-HIV groups (49% and 51%). Overall, HIV infected patients exhibited significantly lower prevalence of RAVs than HIV-uninfected patients (62% vs. 79%, p = 0.03). However, Q80K prevalence was significantly higher in HIV-infected subjects (50% vs. 24%, p = 0.001), whereas prevalence of S122D/G/N/S (2% vs. 16%, p = 0.002) and N174G/N/S (10% vs. 55%, p < 0.0001) polymorphisms were significantly lower. Q80K was found exclusively in clade I viruses. S122 (3% vs. 22%, p=0.001) and N174 (13% vs. 75%, p<0.0001) polymorphisms had significantly lower prevalence in clade I than clade II viruses. CONCLUSIONS: In the Netherlands, prevalence of clade I viruses and Q80K was significantly higher in HCV genotype 1a infected patients with HIV coinfection than in those without HIV coinfection. Prevalence of N174 and S122 polymorphisms was significantly higher in clade II than clade I viruses.