We reviewed the medical charts of 1,700 patients diagnosed with HIV who referred to a central HIV clinic in Tehran between 2004 and 2017. Participants who had a viral load of > 200 copies/mL after six months or more on antiretroviral therapy (ART) were groups as virologic failure (VF). We assessed the demographic characteristics, diagnosis date, first ART regimen, and resistance to various ART drugs. Out of 1,700 patients, 72 (4.2%) had a treatment failure. Among those with treatment failure, 51.3% were on zidovudine + lamivudine + efavirenz, 13.9% were on tenofovir + lamivudine + lopinavir/ritonavir, and 12.5% were on tenofovir + emtricitabine + efavirenz. In patients with treatment failure, the highest resistance was to nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) combination (44.4%). In these patients, resistance to tenofovir (one of the NRTIs) was 29.1%. The highest treatment failure was observed among patients treated with nevirapine (NVP) and efavirenz (EFV)-based regimen. Our findings suggest that protease inhibitors are first-line drugs in ART regimens in VF patients in Iran. Keywords: HIV/AIDS, Virologic Failure, Antiretroviral Therapy, Iran