Antiretroviral resistance testing is an essential tool for the clinical management of Human Immunodeficiency Virus (HIV-1)-infected persons and HIV surveillance in the community. In the absence of appropriate treatment, HIV-1 infection leads toward the collapse of the immune system and death of most HIV-1-infected persons. Adequate antiretroviral treatment usually reverses this process. Nevertheless, HIV-1 easily develops treatment resistance through the accumulation of mutations in its genome. This causes treatment failure, and the requirement of increasingly complex, toxic and expensive treatments. Resistant viruses can be transmitted to other persons. More than 10 % of HIV-1-positive persons in Spain become infected with viruses that are already resistant to at least one antiretroviral drug. Antiretroviral treatment regimens designed on the basis of drug resistance information are more efficacious, effective and efficient.