Magnetic resonance imaging (MRI) and computed tomography (CT) have become essential to diagnostic evaluation of many, or most, important medically and surgically treated diseases. It is important to consider comprehensively the implications in making decisions when choosing one or the other cross-sectional imaging modality. Factors to consider include the relative risks of the contrast agent. Other factors include the relative procedural risks, including radiation risks and the relative expected diagnostic yield of the examination technique (12). In this review we describe both nephrogenic systemic fibrosis and contrast-induced nephropathy to compare the implications with regard to relative risks and benefits of contrast-enhanced MRI or CT in patients with impaired renal function. J. Magn. Reson. Imaging 2009;30:1350-1356. (c) 2009 Wiley-Liss, Inc.