A bstract Introduction Acute kidney injury (AKI) is defined in terms of serum creatinine (SrCrt) and urine output (UO). AKI occurs in 25% of critically ill patients, which increases the risk of morbidity and mortality. Early diagnosis of AKI is challenging, as utility of biomarkers is limited. This study is the first of its kind to estimate urinary potassium (UrK) excretion and its association with AKI in an Indian intensive care unit (ICU). Aims and objectives To study the association between UrK excretion and its ability to predict AKI in ICU patients. Material and methods During this prospective observational study, the patient's urinary indices and renal function tests were measured on day 1 of the ICU admission. UrK excretion and creatinine clearance (CrCl) were calculated from a 2-hour morning urine sample. Association between 2-hour UrK excretion and calculated CrCl and their ability to predict AKI in the subsequent 7 days was evaluated by Kidney Disease Improving Global Outcome (KDIGO)–AKI grading. Results Hundred patients admitted to ICU with a mean age of 53.59 ± 15.8 years were studied. The mean UrK excretion of 4.39 ± 2.52 was correlated linearly with CrCl and has a better prediction to AKI with the area under the receiver-operating characteristic curve value of 0.809 (CI 0.719–0.899), with a significant p -value ( p <0.05). UrK excretion value of 3.49 on day 1 of ICU admission had 87% sensitivity and 74% specificity in predicting AKI. Thirty-one (31%) developed AKI, of which seven (22.58%) required renal replacement therapy (RRT), with 19% of all-cause mortality. Conclusion Diagnosis of AKI with traditional methods is not promising. UrK excretion correlates well with CrCl, which can be considered as the simplest accessible marker for predicting AKI in ICUs. How to cite this article Kumar NS, Kumar GN, Misra KC, Rao M, Chitithoti S, Prakash SY . Association between Urinary Potassium Excretion and Acute Kidney Injury in Critically Ill Patients. Indian J Crit Care Med 2021;25(7):768–772.