Enfuvirtide or T-20 is the first drug approved by the FDA and the EMEA within the group of fusion inhibitors. Its mechanism of action is based on the blockade of the entry of the HIV to the body cells. Enfuvirtide is recommended in combination with other antiretroviral drugs for the treatment of patients infected by HIV that have developed resistance or intolerance to other prior antiretroviral therapies. Clinical trials have shown the effectiveness and safety of the treatment with this drug. Side effects most commonly reported are local reactions in the injection site. Enfuvirtide contributes to increase the therapeutic arsenal available for the management of the HIV infection, providing rescue therapy for patients in which prior treatments have failed.