With the use of combination antiretroviral therapy, the proportion of HIV-infected patients over age 50 has greatly increased. The rate of progression of untreated HIV disease, response to therapy and complicating effects of co-morbidities differ in older versus younger patients. Compared with younger individuals, older untreated HIV patients demonstrate faster rates of CD4+ cell loss and more rapid progression to AIDS and death. With treatment, older patients have a better virological response, but a less robust immunological response. The treatment of older HIV-infected patients is further complicated by pre-existing co-morbid conditions including cardiovascular, hepatic and metabolic complications that may be exacerbated by the effects of HIV infection per se, modest immunodeficiency (i.e. at CD4+ counts >350 cells/mm³), and the metabolic and other adverse effects of combination antiretroviral therapy. Based on these considerations guidelines for the treatment of HIV-infected patients state that increased age is a consideration in initiating antiretroviral therapy in persons with >350-500 CD4+ cells/mm³.