In particular, we found that having 2 CD4<500 cells/mm3 in the first 6 months of HIV diagnosis was associated with a probability of being alive and AIDS-free at 4 years of HIV seroconversion of 60% (95% CI 50%,68%), lower than the estimated 86% (77%,92%) for individuals without a CD4<500 cells/mm3 at that time. This evidence concerns the gene CD4 and AIDS.