Severe sepsis is one of the leading causes of acute kidney injury (AKI). Patients with sepsis-associated AKI demonstrate high-hospital mortality. We evaluated the incidence of severe sepsis-associated AKI and its association with outcome in intensive care units (ICUs) in Finland. Methods This was a predetermined sub-study of the prospective, observational, multicentre FINNAKI study conducted in 17 ICUs during 1 September 2011 and 1 February 2012. All emergency ICU admissions and elective admissions exceeding 24 hours in the ICU were screened for presence of severe sepsis and AKI up to 5 days in ICU. AKI was defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria and severe sepsis according to the American College of Chest Physicians/Society of Critical Care Medicine (ACCP/SCCM) criteria. Results Of the 2901 included patients, severe sepsis was diagnosed in 918 (31.6 , 95 confidence interval [CI] 29.9-33.4 ) patients. Of these 918 patients, 488 (53.2 [95 CI 49.9-56.5 ) had AKI. The 90-day mortality rate was 38.1 (95 CI 33.7-42.5 ) for severe sepsis patients with AKI and 24.7 (95 CI 20.5-28.8 ) for those without AKI. After adjusting for covariates, KDIGO stage 3 AKI was associated with an increased risk for 90-day mortality with an adjusted odds ratio (OR) of 1.94 (95 CI 1.28-2.94), but stages 1 and 2 were not. Conclusions More than half of the patients with severe sepsis had AKI according to the KDIGO classification, and AKI stage 3 was independently associated with 90-day mortality.