Anthropometric data were collected on 89 children born to human immunodeficiency virus (HIV)-infected women (37 who seroreverted and 52 who were HIV-infected). The main outcomes included birth weight, gestational age, weight, height, arm muscle circumference (AMC), and triceps skinfold thickness (TSF). Gestational age and birth weight were not different between the two groups. The earliest anthropometric evaluation on seroreverted children (age 19 mo) when compared with HIV-infected children (age 21 mo) revealed that weight and weight-for-height percentiles were significantly different (51% vs 33% and 66% vs 48%, respectively). Height and TSF percentiles were not different, although AMC percentiles were lower in infected children (64% vs 43%). In follow-up evaluations, the weight differences between infected and control children did not change. We conclude that HIV does not affect birth weight, but postnatal events result in altered weight gain in HIV-infected children. Lean body mass is lower than in an HIV-negative comparison group at early stages of HIV infection.