The prevalence of maternal respiratory syncytial virus (RSV)-neutralizing antibodies has been documented in developed countries, but there is little information from developing countries. We assessed the prevalence of RSV-neutralizing antibody in sera from Gambian women and their newborns and compared them with their American counterparts during a similar period. The geometric mean titers of maternal antibodies to RSV subgroup A in the two populations were similar, while titers of antibodies to RSV subgroup B in Gambian mothers were significantly higher (8.7 +/- 1.4 versus 7.9 +/- 1.3 [mean +/- standard deviation], P < 0.001). The titers of neutralizing antibody in newborns in both populations correlated with the neutralizing-antibody titers of their mothers. Thus, the status of neutralizing antibody to both major RSV subgroups was comparable among infants and mothers in a developing country, The Gambia, and those in a developed country, the United States.