Immune activation is a hallmark of disease progression in human immunodeficiency virus (HIV) type 1 (HIV-1) and HIV type 2 (HIV-2) infection. However, the relationship between viremia and systemic immune activation is unclear. We assessed the relationship between HIV-2 plasma virus load and immune system activation in a cross-sectional study in a community cohort of HIV-1-positive, HIV-2-positive, and HIV-negative patients, in which many HIV-2-positive patients had nonprogressing infection. HLA-DR and CD38 expression on CD4(+) and CD8(+) T cells was measured, as were plasma beta(2)-microglobulin levels. These markers were related to clinical (virus load and CD4(+) cell count) and immunological (HIV-2-specific interferon gamma secretion) correlates of delayed disease progression. A consistent positive correlation was identified between the level of HIV-2 viremia and immune activation. We propose that increasing virus load may contribute to systemic immune activation in HIV-2 infection.