Morbidity and mortality associated with HIV infection increased rapidly following the recognition of this syndrome in 1981, and by 1994, AIDS was the leading cause of death in the United States among men and women ages 15-45. The antiretroviral therapy era began in 1987 following the Food and Drug Administration approval of zidovudine, a nucleoside analog reverse transcriptase inhibitor; however, it was not until 1996, when HIV viral load assays were developed that could quantify the copy number of HIV RNA present in plasma, that investigators and clinicians could appropriately evaluate the antiviral efficacy of therapy. This important technical breakthrough and the availability of HIV protease inhibitors led to a dramatic decline in the morbidity and mortality associated with the disease.