An epidemic of Ross River Virus (RRV) occurred in the South Pacific in 1979-1980, but it was not believed to occur endemically outside Australia and Papua New Guinea. We conducted a seroprevalence study to determine whether RRV has circulated in American Samoa after 1980.RRV ELISA IgG were performed on 200 serum samples collected in American Samoa in 2010, and seroneutralisation tests on 60 representative samples.Of 196 results available for ELISA IgG, 145 (74%, 95% CI 67-80%) were seropositive. Of 60 samples subjected to seroneutralization, none of the 15 ELISA IgG-negative and 16 of the 45 ELISA IgG-positive samples neutralized RRV. ELISA IgG seroprevalence was higher in persons born before/during the 1979-1980 RRV outbreak (78.3%), but was also high (63.0%) in people born after the outbreak and had lived their whole lives in American Samoa.Our study provides serological evidence that RRV circulation is likely to have occurred in American Samoa after 1980. Considering there are no marsupials in American Samoa, our findings imply that other species are capable of acting as reservoir hosts, and the potential for RRV to circulate in a much wider area than the currently recognised locations.