Accurate preoperative assessment of renal and perirenal tumors is crucial in determining the type of therapy and/or in planning the operative approach. Computed tomography has been used extensively to stage renal cancer by defining the extent of disease within and outside the kidney, demonstrating patency of the renal vein and inferior vena cava, and depicting sites of lymph node involvement. Recent studies have shown magnetic resonance imaging to be comparable or superior to computed tomography in staging renal carcinoma. Because of its multiplanar imaging capabilities, MRI has also proven useful in evaluating perirenal masses that may obstruct, displace, or invade the kidney. The advantages and limitations of MRI and CT are discussed and their current roles in the evaluation of renal and perirenal abnormalities are reviewed.