Neutrophil, lymphocyte, and T-cell subset numbers and immunoglobulin levels were evaluated at birth to age 2 years in 675 children born to mothers infected with the human immunodeficiency virus type 1 (58 infected symptom-free subjects (P-1), 203 infected subjects with symptoms (P-2), and 414 uninfected subjects). The P-2 patients had (even at birth to age 1 month) lower CD4+ lymphocyte and higher IgA and IgM values than P-1 and uninfected children had. Increased IgG values (from 1 to 6 months of age) and increased CD8+ lymphocyte numbers (at 13 to 24 months of age) were also observed. The P-1 children differed from uninfected children only at 13 to 24 months of age (decreased CD4+ and increased CD8+ lymphocytes). Progressive immunologic changes were found in P-2 patients who had severe clinical conditions and in those who died. To evaluate the predictive meaning of the immunologic changes, we selected 164 children (25 P-2, 15 P-1, and 124 uninfected children) because they had been examined sequentially from birth and they were classified as in the indeterminate state of infection (P-0) at immunologic evaluations at birth to age 1 and at 1 to 6 months of age. During the 1- to 6-month period, P-2 patients had higher immunoglobulin and lower CD4+ lymphocyte values than P-1 and uninfected children had; no difference was found between P-1 and uninfected subjects. These results indicate that in infants with perinatal human immunodeficiency virus type 1 infection, immunologic abnormalities correlate with the clinical condition and are predictive of the clinical outcome rather than the infection status.