Most renal masses and cysts are adequately characterized by ultrasonography or computerized tomography. Occasionally, further diagnostic evaluation is needed. Magnetic resonance imaging has emerged as the premier study to evaluate suspected tumor thrombus and to plan the operative technique in challenging cases. Intraoperative ultrasonography is a valuable real-time imaging modality for delineating tumor extent and margins during nephron-sparing surgery and in evaluating the presence of synchronous multifocality. Additionally, localized central renal tumors can be treated with ultrasonography-guided radiofrequency ablation. Positron emission tomography has little use in the diagnostic evaluation of renal masses, but may be useful in staging equivocal cases and in evaluating suspected recurrence or metastases in patients after nephrectomy for renal cell carcinoma.