Traditionally, KS has been associated with advanced age or with significant immunosuppression. We recently reported an atypical cohort of antiretroviral-treated HIV infected patients who developed cutaneous KS despite having undetectable plasma HIV RNA levels and high CD4+ T cell counts. The KS lesions seen in these patients were indolent and reminiscent of classical KS seen in the HIV-negative elderly. The mechanism of KS in the elderly remains undefined, but many have postulated a potential role of immunosenescence, which is generally defined as the gradual loss of immunologic function during advanced age. Given emerging evidence suggesting that prolonged periods of untreated HIV infection results in accelerated and perhaps irreversible "aging" of the immune system, we hypothesized that immunosenescence may account for the development of KS in otherwise young well-treated HIV infected individuals.