Rotavirus vaccine for infants was introduced into the National Immunisation Program in Australia in July 2007. To determine the impact of rotavirus vaccination on gastroenteritis hospitalisations amongst children less than six years of age in South Australia, we conducted a retrospective analysis of hospital admissions over two time periods: 1 May 2005-30 April 2007 (prior to rotavirus vaccination introduction) and 1 May 2008-30 April 2010 (post rotavirus vaccination introduction). The introduction of rotavirus vaccination has been associated with a marked reduction in hospital admissions for serious rotavirus gastroenteritis (RVGE) and all-cause gastroenteritis (ACGE). Following the introduction of rotavirus vaccination in South Australia, there was an 83% reduction in RVGE coded admissions (955 vs 165) and a 48% reduction in ACGE coded admissions (4153 vs 2142) for children aged less than six years. Children less than two years demonstrated the greatest reduction (90%) in RVGE admissions and ACGE admissions (57%). Age-specific RVGE hospitalisation rates decreased from 933/100,000 prior to rotavirus vaccine introduction to 88/100,000 for children less than two years of age. In addition, for gastroenteritis hospitalisations for children aged five years at time of admission (unvaccinated cohort) there was a reduction in the number of RVGE cases (24 vs 4), a reduction in age-specific RVGE hospitalisation rates (65/100,000 vs 11/100,000) and a significant reduction in the proportion of overall gastroenteritis cases which were rotavirus positive (11.5% vs 3.5%), suggesting a positive impact on both unvaccinated and vaccinated children less than six years of age in South Australia. ; Michelle F. Clarke, Geoffrey P. Davidson, Michael S. Gold, Helen S. Marshall