HIV resistance to antiretroviral drugs was studied in 348 samples taken from patients at the Molecular Biology Unit of the Microbiology Department of the Hospital La Fe, from January 2003 to July 2007. Once the viral load in plasma was determined, resistance was detected using complete gene sequencing for protease up to position 3464 of the HIV-1 reverse transcriptase gene. The results were analyzed using the Omiga 1.2 (Oxford Molecular Group) and HIV db Genotypic Resistance Interpretation Algorithm Version 4.3.0 (Stanford University) programs. The drugs least affected by the presence of mutations leading to resistance were the protease inhibitors darunavir, tripanavir and lopinavir (sensitivity >80%), the nucleoside reverse transcriptase inhibitors tenofovir and lamivudine (sensitivity >90%) and the non-nucleoside reverse transcriptase inhibitor TMC125 (sensitivity >80%).