Background and Objectives There is little data on the duration of viraemia following infection with Ross River virus (RRV), the most common cause of arbovirus disease in Australia. In particular, no accurate estimate exists for the duration of pre-symptomatic RRV infection, which is important in assessing the potential for transfusion transmission. Materials and Methods We used an established mouse model of RRV infection involving adult Swiss outbred mice to measure viraemia following infection. Applying our experimental data to a published probabilistic model for estimating the risk of dengue transmission by transfused blood, we derived comparable risk estimates for RRV. Results Ross River virus RNA was measured using highly sensitive real-time PCR in serum samples to determine the duration of asymptomatic viraemia, which typically lasted 5 days, but extended to 9 days in some mice. Assuming the potential for transfusion transmission is proven, the risk of RRV transmission by blood during a 2004 outbreak in Cairns, Australia was retrospectively estimated as 1 in 13 542 (range from 1 in 4765 to 47 563). Conclusion This study provides updated epidemiological data useful to underpin modelling to assess the potential risk of transfusion-transmitted RRV. Using an established model for dengue, the risk estimate for RRV transmission is comparable in the same geographical region. Should transfusion be proven as a route of transmission, this supports consideration of appropriate mitigation strategies to safeguard blood recipients.