The natural history of HIV-1 infection in children has not yet been determined precisely. Contrary to what is observed in adults, the disease seems to follow a bimodal course. One-quarter to one-third of infected children develop, before the end of their first year of life, a deep immunodeficiency which is responsible for severe infectious and neurological symptoms; survival does not exceed 4 to 5 years. In contrast, although the other children are symptomatic, their disease progresses much more slowly, perhaps as slowly as in adults, and their long-term outcome remains uncertain.