The CCR5 chemokine receptor is required by non-syncytium HIV-1 strains to infect target cells. A 32 base pair deletion (delta32) in the CCR5 gene causes a structural CCR5 modification that does not permit HIV-1 entry into cells. The rate of the CCR5 delta32 was investigated in 137 children born from HIV-infected mothers. Overall, five (10.6%) of 47 HIV-infected infants showed the defect in heterozygosis vs. eight (8.9%) of 90 uninfected children. No CCR5 delta32 homozygotes were found. Interestingly, among infected children, five (21.7%) of 23 showing a slow disease progression were heterozygous for the CCR5 delta32, meanwhile none of the 24 infants with rapid disease course had the deletion (P = 0.022). In conclusion, the CCR5 delta32 defect does not protect against vertical HIV-1 transmission, but is associated with a delayed disease progression in HIV-infected children.