Diffusion-weighted (DW) magnetic resonance imaging (MRI) is a functional imaging technique that derives image contrast from differences in water molecule diffusion within tissues. DW MRI helps detect and characterize renal and urothelial malignancies, may help in differentiating some benign from malignant renal masses, and can also recognize renal and upper urinary tract infections. Patients precluded from receiving intravenous contrast agents may particularly benefit from this technique.