To assess the characteristics, treatments and outcomes of paediatric and adult intensive care unit (ICU) patients with respiratory syncytial virus (RSV) infection, and compare these with coronavirus disease (COVID-19) during the same period.We conducted a multicenter, prospective, observational study using data from the short period incidence study of severe acute respiratory infection (SPRINT SARI) Australia, in 38 Australian ICUs from 1 June 2022 to 1 September 2024. Demographic, treatment, and outcome data were analysed for patients with confirmed RSV or COVID-19. The primary outcome was in-hospital mortality.Of 4693 patients were recorded in the SPRINT-SARI database, 2540 met inclusion criteria. RSV was more common in paediatric patients (410/620, 62%) than in adults (249/1920, 13%). Adult with RSV had more chronic pulmonary conditions than those with COVID-19. Paediatric patients with RSV had fewer comorbidities and less invasive mechanical ventilation (IMV) compared to those with COVID-19 (P < 0.05), but required longer duration of IMV once intubated. In-hospital mortality was similar for both adult RSV and COVID-19 (36/249, 14.5%) vs (260/1671, 15.6%), and paediatric RSV(3/410 [0.7%] vs 7/210 [3.3%] P = 0.07). Mortality in adults was associated with male sex, older age, comorbidities, and IMV. Mortality in children was associated with IMV only.RSV infection can result in an attributable number of ICU admission in Australia, especially in specific populations including young children and older adults with respiratory comorbidities. Mortality in patients admitted to ICU is similar to COVID-19.