 The renal resistive index, RRI, is a measure of the resistance to blood flow through the kidneys. It is used as a diagnostic tool to detect kidney disease and can also be used to predict the outcome of renal artery stenosis treatment. Additionally, it has been found to be useful in predicting the progression of chronic kidney disease and the survival rate of renal transplants. Furthermore, it has been shown to correlate with other markers of systemic cardiovascular health such as pulse pressure and vascular compliance. This article was authored by Roxana Deribont, Diana Mehalsia, and Drago Svidharianu.