Relative resistance to HIV infection has been associated with genetic polymorphisms. Both single nucleotide polymorphisms and copy number variations (CNVs) have been documented for defensins, which are natural inhibitors of HIV infection. We tested the hypothesis that these CNVs may be related to susceptibility to HIV infection and vertical transmission by evaluating the CNVs of 13 defensin genes in Brazilian HIV-infected children. Study groups included seronegative controls, HIV-infected subjects, and subjects who did not contract HIV despite exposure at the time of birth from HIV-infected mothers. We observed that the copy number of one of these genes, DEFB104, was significantly lower in HIV-positive subjects than in HIV-exposed uninfected children, suggesting DEFB104 as a candidate HIV-protective gene.