OBJECTIVE To determine the relationship between CD4 status and the P24 antigen level and survival in children infected with the human immunodeficiency virus. METHODS Cohort, case-control. METHODS Clinical Center at the National Institutes of Health, Bethesda, Md. METHODS One hundred forty-seven children infected with the human immunodeficiency virus enrolled in antiretroviral therapy protocols at the National Cancer Institute were reviewed and the relationships between CD4 counts, P24 antigenemia, and death were analyzed. METHODS None. RESULTS The presence of a very low CD count, less than 21% of the lower limit of normal values for age (equivalent to 0.05 x 10(9)/L in an adult), was associated with a significantly increased risk of death within 2 years. Although the risk of death was highest for children with CD4 counts below this level and who had detectable P24 antigen levels, P24 antigenemia by itself contributed little to the prognostic value of the CD4 count alone. However, it was also notable that a group of children with low CD4 counts also experienced prolonged survival. CONCLUSIONS The association between low CD4 counts and death suggests that the age-adjusted CD4 count should be used as a marker to guide therapeutic intervention. At the same time, the presence of a very low CD4 count alone should not be considered a reason for therapeutic nihilism.