This study investigated coexpression of CD28, CD45RA, and CD45RO on CD4(+) and CD8(+) cells in 107 human immunodeficiency virus (HIV) type 1-infected patients, who were followed-up prospectively and were not treated with highly active antiretroviral therapy, and 65 control subjects. The most important novel finding was that a 50% reduction in CD4(+)CD28(+) cells predicted increased mortality (relative hazards [HR], 1.6; 95% confidence interval [CI], 1.0-2.6; P=.04), even after adjusting for the CD4(+) cell counts, virus load, beta(2)-microglobulin and hemoglobin levels, and HIV disease stage. Patients with progressed HIV infection had decreased concentrations of all studied cell subsets. Concerning the proportions of cells, only CD4(+)CD28(+), CD4(+)CD45RA(+), and CD8(+)CD45RO(+) cells decreased with HIV progression. Low proportions of CD4(+)CD45RA(+), CD8(+)CD45RA(+), and CD8(+)CD45RO(+) cells predicted mortality only in univariate but not in multivariate Cox analyses. If our results are confirmed in other studies, coexpression of CD28 on CD4(+) cells may be a useful marker to evaluate HIV progression.