Cystic renal masses are commonly encountered in clinical practice. Improved resolution of imaging modalities has in part led to the improved ability to detect these abnormalities. Yet the Bosniak criteria have stood the test of time as radiologists and urologists still primarily rely on these. Нe conventional CT and MRI sequences cannot easily diوٴerentiate benign from malignant lesions in many cases. Studies have shown that 16%-33% of nephrectomies are performed on benign lesions . Нere is also a strong need for alternatives to gadolinium-enhanced sequences in patients at risk for nephrogenic systemic ٽbrosis (NSF) . Percutaneous biopsy of renal tumors has been widely demonstrated to be an accurate method of diagnosing preoperative pathologic subtypes in many patients. However, the risk of procedural complications and the potential for sampling error have hindered universal acceptance of percutaneous biopsy. Нe basic physical principle of diوٴusion-weighted imaging is based on the random movements of molecules (Brownian motion) in a spatial plane. Нis is aوٴected by diوٴerences in the nucleocytoplasmic ratio and factors that change water diوٴusion in the interstitial space such as increased cell density and viscosity. DWI has become more familiar and has gained a deٽnitive role in the characterization of abdominal malignancy in lymph nodes, and renal, liver, pancreas, prostate masse.