Retroperitoneal fibrosis (RPF) encompasses a range of diseases characterized by proliferation of aberrant fibroinflammatory tissue, which usually surrounds the infrarenal portion of the abdominal aorta, inferior vena cava, and iliac vessels. This process may extend to neighboring structures, frequently entrapping and obstructing the ureters and eventually leading to renal failure. The idiopathic form of RPF accounts for more than two-thirds of cases; the rest are secondary to factors such as drug use, malignancies, or infections. If promptly diagnosed and treated, idiopathic and most other benign forms of RPF have a good prognosis. In contrast, malignant RPF, which accounts for up to 10% of cases, has a poor prognosis. Therefore, the most important diagnostic challenge is differentiation of benign from malignant RPF. Imaging plays a key role in diagnosis of RPF. Cross-sectional imaging studies, particularly multidetector computed tomography (CT) and magnetic resonance (MR) imaging, are considered the imaging modalities of choice. Imaging features may help distinguish between benign and malignant RPF, but in some cases histopathologic examination of the retroperitoneal tissue is needed for definitive diagnosis. CT and MR imaging, along with positron emission tomography with fluorine 18 fluorodeoxyglucose, also play an important role in management and follow-up of idiopathic RPF.