HIV-1 RNA was measured within 4 days after birth in 98% of women who delivered during the study period, with one subsequent measurement during breast-feeding in 99.7% of the women who breast-fed. Among live-born infants, 99.6% had a known HIV-1 infection status at birth (three died shortly after birth without having undergone testing). A final HIV-1 infection status was confirmed in 95% of infants at either 6 months or within 1 day after death. One infant died after a single positive PCR test at birth. The remaining 5% tested negative on at least one occasion before 6 months or before death from a non−AIDS-related illness. Three percent of infants were withdrawn from the study before 6 months for a reason other than death.