The recent technical developments in magnetic resonance imaging (MRI) and the use of paramagnetic contrast media (gadolinium compounds) have considerably improved the performances of MRI for the detection and characterization of renal tumors. MRI does not have specific merits for the diagnosis of the typical form of cancer, nor for the detection of small kidney tumors, both being mainly based on computed tomography (CT). On the other hand, it can be used for the diagnosis of atypical forms of cancers (small, hypovascular, cystic or hemorrhagic cancers) which raise problems of differential diagnosis with some pseudotumoral lesions, complex cysts and benign tumors. Its complementarity to CT for the characterization of an atypical mass results from the signal information it provides, from a better contrast resolution, and from the possibility to make sections in all planes of space. Except for angiomyolipoma, which has a fatty content, there is no really specific MR criterion as present to evidence benign renal tumors. Concerning regional extension, CT remains the primary technique of choice, as it allows studying the limits of the tumor, the renal compartment and its walls, the renal vein and the inferior vena cava, the neighboring organs and the contralateral kidney all together. Its findings allow defining the indications of MRI, which, as a complementary exploration, is often decisive to assess venous invasion.