Acute HIV infection, essentially indistinguishable from a “flu-like” illness, usually goes unrecognized but is reported to occur in 50% to 90% of patients. The time from exposure to onset of symptoms is usually 2 to 4 weeks, and the most common symptoms include fever (> 90%), fatigue (70% to 90%), sore throat (> 70%), rash (40% to 80%), headache (30% to 80%), and lymphadenopathy (40% to 70%). Other reported symptoms include myalgias, diarrhea, and weight loss. Seroconversion, reflecting detectable antibody response to HIV, usually occurs 3 to 8 weeks after infection. This is followed by a long period of asymptomatic infection except for possible persistent generalized lymphadenopathy. Early symptomatic infection is characterized by conditions that are more common and more severe in the presence of HIV infection but, by definition, are not AIDS indicator conditions. Examples include thrush, persistent vulvovaginal candidiasis, peripheral neuropathy, cervical dysplasia, recurrent herpes zoster infection, and idiopathic thrombocytopenic purpura. At this time CD4 counts are 200 to 500 cells/mm3. As the CD4 count drops below 200 cells/mm3, the frequency of opportunistic infections dramatically increases. AIDS is defined by the appearance of any indicator condition (Table 92-1) including a CD4 count lower than 200 cells/mm3. Late symptomatic or advanced HIV infection exists in patients with a CD4 count lower than 50 cells/mm3 or clinical evidence of end-stage disease, including disseminated Mycobacterium avium complex or disseminated cytomegalovirus (CMV). In today's era of highly active antiretroviral therapy (HAART), longevity is more dependent on age and other comorbidities than HIV status provided the patient adheres to HAART and the therapy is effective in suppressing viral load and maintaining normal CD4 counts.