Children infected with HIV display great variability in their clinical outcome and rate of progression to AIDS. The reasons for this variability are largely unknown. Increasing evidence from adult studies suggests that the cellular immune response is a critical determinant of viral containment, and likely accounts for much of the observed variability in clinical progression. Detailed studies of the HIV-specific immune responses generated by adults with long-term nonprogressive infection have revealed elements of the host immune response that correlate with effective viral control. However, much less is known about the HIV-specific immune responses generated by perinatally infected children. Recent studies have revealed that elements of both the HIV-specific cytotoxic T lymphocyte response (mediated by CD8+ lymphocytes) and the T-helper response (mediated by CD4+ lymphocytes) differ between adults and children, and these differences could have important implications for the ability to control HIV viraemia. Identification of the precise correlates of viral containment in children could provide important insights into the pathogenesis of vertical infection, and will greatly assist the rational design of HIV vaccines and immunotherapies.