Primary varicella infection, or chickenpox, can be devastating to HIV-infected children because complications occur at higher rates in immunocompromised hosts. Current passive prophylaxis measures with varicella-zoster immune globulin are suboptimal because administration must be repeated for each exposure during the child's lifetime and timely notification of exposure is not always possible. Since Varivax has been licensed for routine vaccination of healthy individuals, it must be determined whether this vaccine can be safely administered to HIV-infected children.