BACKGROUND The heterogeneity of CD4 T-cell counts and HIV-1 RNA at 5-12 years after the initiation of highly active antiretroviral therapy (HAART) remains largely uncharacterized. METHODS In the Multicenter AIDS Cohort Study, 614 men who initiated HAART contributed data 5-12 years subsequently. Multivariate regression was used to evaluate the predictors of CD4 counts and HIV-1 RNA levels. RESULTS At 5 to 12 years post-HAART, the median CD4 T-cell count was 586 (interquartile range, 421-791) cells per microliter and 78% of the HIV-1 RNA measurements were undetectable. Higher CD4 T-cell counts 5-12 years post HAART were predicted by higher CD4 T-cell counts and higher total lymphocyte count pre HAART, lack of hepatitis B or C virus coinfections, and greater CD4 T-cell change and suppressed HIV-1 RNA in the first 5 years after starting HAART. Men who were 50 years and older with 351-500 CD4 cells per microliter at HAART initiation had adjusted mean CD4 T-cell count of 643 cells per microliter at 10-12 years post HAART, which was similar to the adjusted mean CD4 T-cell count (670 cells/μL, P = 0.45) in this period for younger men starting HAART with lower CD4 T-cell counts. HIV-1 RNA suppression in the first 5 years post HAART predicted subsequent viral suppression. CONCLUSIONS Immunological and virological responses in the first 5 years post HAART predicted subsequent CD4 T-cell counts and HIV-1 RNA levels. The association between age and subsequent CD4 T-cell count supports incorporating age in the guidelines for use of HAART.