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Several studies have reported an increasing number of therapeutic failures with antiretroviral drugs in HIV-infected patients. The emergence of viral-resistant strains is a major problem for the medical management of infected individuals. The aim of this study is to determine viral subtypes and drug-resistance mutations among antiretroviral-treated HIV-infected patients.A total of 42 antiretroviral-treated but still viremic HIV-infected patients were enrolled. The HIV pol regions were amplified and sequenced to determine subtypes and antiretroviral-resistant mutations.The subtype distribution was 48% A/D recombinants, 43% subtype B, 5% subtype A and 5% CRF01-AE recombinants. Drug-resistant mutations were most common in subtype B (53%) and A/D recombinant strains (44%). Virus samples from 19% of participants had no drug-resistant mutations; 2, 2 and 76% of samples carried one, two and at least three drug-resistant mutations, respectively. The prevalence of nucleoside transcriptase inhibitor mutations was 76%, with M184V and L74V present in 60 and 38% of samples, respectively. The prevalence of nonnucleoside transcriptase inhibitor mutations was 74%, with P225H present in 55% of study specimens. The prevalence of protease inhibitor mutations was 45%, with major mutation L90M seen in 33% and minor mutation A71V in 36% of samples. Of note, the P225H and A71V are ‘minor’ drug-resistance mutations conferring only minimal drug-resistance phenotypes in the absence of major mutations.Our study found a high prevalence of drug-resistant mutations in Iranian HIV-infected patients. Our data support the need for continued surveillance of resistance patterns to help guide therapeutic approaches and limit transmission of these variants.