Objective: To compare the unprecedented 91 cases of melioidosis in the Top End of the Northern Territory of Australia from 1 October 2009 to 30 September 2010 with the 540 cases in the preceding 20 years and postulate reasons for this year of very high melioidosis incidence. Design, setting and participants: Review of prospectively collected data on all patients with culture-confirmed melioidosis at Royal Darwin Hospital, the Top End's tertiary referral centre, since 1 October 1989. Main outcome measures: Population-based annual incidence of melioidosis; differences in epidemiology, clinical presentations and outcomes for 2009- 2010 compared with the preceding 20 years. Results: In 2009-2010, the estimated population-based incidence of melioidosis was 50.2 cases per 100 000 in the Top End population overall, and 102.4 cases per 100 000 in the Top End Indigenous population. The proportion of patients acquiring melioidosis in the Darwin urban area increased from 49% in 1989-2009 to 65% in 2009-2010 (OR, 1.96; 95% CI, 1.20-3.19). Among the 49 Indigenous Australian patients with melioidosis in 2009-2010, 63% acquired the infection in Darwin, compared with 35% of Indigenous patients in the previous 20 years (OR, 3.17; 95% CI, 1.62-6.24). Conclusions: In 2009-2010, the Top End had the highest annual incidence of melioidosis documented from anywhere to date. The prominent increase in cases in Darwin was associated with above average rainfall in Darwin during December 2009 to February 2010. The increase in the proportion of Indigenous Australians who acquired melioidosis in Darwin may reflect movement of some Indigenous people into Darwin from remote communities.