9570 Background: Although cancer patients may be at increased risk for acute kidney injury (AKI), which could then reduce their likelihood of receiving optimal therapeutic management and supportive care, the occurrence of AKI among newly diagnosed cancer patients has not been well-described. Therefore, we examined the incidence of AKI within the first year after cancer diagnosis to estimate the magnitude of this risk and better understand which patients are at greatest risk. Methods: Using the population-based Danish Cancer Registry, we conducted a retrospective cohort study of 4,427 men and women from North Jutland, Denmark (population 500,000) diagnosed with cancer from 2002 to 2003 (non-melanoma skin cancer excluded). AKI was defined according to the Risk/ Injury/ Failure/ Loss/ End-stage-renal-disease (RIFLE) criteria. We included Risk or worse: at least a 1.5 times increase in serum creatinine (sCr) from baseline. SCr levels were obtained from the Regional Laboratory Database, which collects all biochemical analyses for hospital laboratories. Baseline sCr was defined as the lowest sCr in the year before cancer diagnosis. We compared this value to the highest sCr on record during the first year following cancer diagnosis to identify those who experienced an AKI. Results: Median age for the cohort was 68.6 years, 50.9% were men, and the most common cancer sites were lung (14.2%), breast (13.7%), prostate (9.8%), colon (9.6%), rectum (5.1%), and bladder (6.3%). During the first year, 973 (22.0%) members of the cohort experienced an AKI, corresponding to an overall incidence rate of 326 per 1,000 person-years (95% confidence interval (CI) 306–347). Incidence was highest among patients aged 80 years or older (531 per 1,000 person-years, 95% CI 464–606) and in those with cancer of the liver (1,221, 95%CI 676–2,205), pancreas (1,472, 95%CI 1,130–1,917), or kidney (1,254, 95%CI 974–1,616), or with multiple myeloma (855, 95%CI 538–1,356). Conclusions: To protect against AKI, we must first identify those at risk. Our study showed that over 20% of cancer patients may experience acute kidney injury in the first year after diagnosis. Older patients and those with cancer of the liver, pancreas, or kidney, or with multiple myeloma are especially at risk for AKI. [Table: see text]