We analyzed the effect of age on highly active antiretroviral therapy efficacy and tolerance in 639 patients with human immunodeficiency virus (HIV) infection (99 of whom were aged >50 years, and 540 of whom were aged <50 years). Late testing, which was more frequent in the older age group, was the only independent factor associated with immunologic and clinical evolution of infection. Age >50 years was associated with earlier treatment discontinuation.