CD4+ and CD8+ T lymphocyte counts, naive and memory/effector CD4+ T subpopulations, and the expression of CD38 on CD8+ T lymphocytes were evaluated in four groups: AIDS patients with tuberculosis (HIV/TB, n=14), HIV-1 infected patients (HIV, n=10), HIV-1 negative patients with tuberculosis (TB, n=20) and healthy controls (CTL, n=17). TB and HIV had fewer CD4+ T cells than CTL, with the lowest values observed in TB/HIV (p<0.001). No difference between groups was observed in the percentage of naive and memory/effector subpopulations in CD4+ T lymphocytes. TB (355 cells/mL) and HIV (517 cells/mL) had diverging effects on CD8+ T cell counts, with a marked depletion observed in HIV/TB (196 cells/mL). TB and HIV up-regulated CD38 expression on CD8+ T cells, a finding also present in TB/HIV. While the decrease of CD4+ T cell counts in HIV/TB may be attributed to HIV and tuberculosis, the decrease of CD8+ T cell counts is likely to be due to tuberculosis.