Abstractobjective Invasive group A streptococcus (iGAS) disease is an important cause of mortality globally. The incidence of iGAS in Australia's tropical Northern Territory (NT) has been previously reported as 32.2/100 000 in Indigenous people for the period 1991-1996. We aimed to measure the incidence and severity of iGAS disease in the NT since this time.methods We collected demographic data for all GAS blood culture isolates over a 12-year period (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) from the three hospital laboratories serving the tropical NT. We then collected detailed clinical information from hospital records and databases for the subset of these patients who were admitted to Royal Darwin Hospital during [2005][2006][2007][2008][2009].results There were 295 confirmed cases of GAS bacteraemia over the study period, with a mean (SD) age of 42.1 (22.0) years, and 163 (55.0%) were male. The annual age-adjusted incidence was 15.2 (95% CI 13.4-16.9)/100 000 overall and 59.4 (95% CI 51.2-67.6) in Indigenous Australians. ; 29 patients (23.6%) required intensive care unit admission and 20 (16.3%) had streptococcal toxic shock syndrome. Antecedent sore throat or use of non-steroidal anti-inflammatory drugs was rare, but current or recent scabies, pyoderma and trauma were common.conclusion The incidence and severity of iGAS are high and increasing in tropical northern Australia, and urgent attention is needed to improve surveillance and the social determinants of health in this population. This study adds to emerging data suggesting increasing importance of iGAS in low-and middle-income settings globally.