We determined whether polymorphisms in Fcγ receptor (FcγR) IIa or FcγRIIIa genes were associated with outcomes in Vax004, a trial testing recombinant gp120 vaccination in preventing sexually acquired HIV infection. Male subjects (n = 1725), including infected and uninfected vaccinees and placebo recipients, were genotyped. We observed no association between FcγRIIa genotype and infection rate in vaccinees or placebo recipients. However, FcγRIIIa genotype was associated with infection rate among vaccinees (P = .035). Exploratory analyses revealed that vaccinees homozygous for the FcγRIIIa V allele in the lowest behavioral risk group had a greater rate of infection than low risk vaccinees with at least 1 F allele (hazard ratio [HR] = 3.52; P = .002). No such association was seen among vaccinees with high-risk behaviors or among placebo recipients in either risk stratum. Vaccinated low-risk VV subjects had a greater infection rate than low-risk VV placebo recipients (HR = 4.51; P = .17) or low-risk placebo recipients with any genotype (HR = 4.72; P = .002). Moreover, low-risk VV vaccinees had infection rates similar to individuals with high behavioral risk, irrespective of genotype. Our results generate the hypothesis that recombinant gp120 vaccine may have increased the likelihood of acquiring HIV infection in individuals with the VV genotype (present in ∼ 10% of the population) at low behavioral risk of infection.