More renal tumors are now being found at an early stage. Similarly, the treatment of patients with such small tumors is shifting away from radical nephrectomy toward nephron-sparing extirpative surgery or nonextirpative renal tumor ablation. Of the various techniques used for renal tumor ablation, cryotherapy is the most extensively studied and has the longest reported outcomes. In this article, we examine the experimental and clinical evolution of cryotherapy for small renal masses. A literature search was performed with the following key words: cryobiology, cryotherapy, cryoablation, tissue-ice interaction, temperature, monitoring, cryoinjury, renal function, blood pressure, and treatment end point. Articles that dealt with the experimental and clinical bases of current cryoablation principles and techniques were selected for review. Some recent studies representative of current clinical outcomes were also examined. Cryotherapy for the small renal tumor can be performed during open surgery, laparoscopically, or even percutaneously with use of a variety of probes and high-resolution imaging techniques to monitor therapy. In the clinical scenario, the ice ball is usually extended 1 cm beyond the visible tumor margin. Cryotherapy per se does not adversely affect renal function and blood pressure. Inadvertent cryoinjury to the collecting system rarely leads to urinary leakage. To date, only 6-month follow-up biopsy data are available. Absence of contrast enhancement on follow-up computed tomography or magnetic resonance imaging is considered oncologic success. For a sporadic unilateral renal tumor, 98% cancer-specific survival at 3 years has been reported. Cryotherapy has moved beyond the "experimental" stage, and initial outcomes are encouraging. The major criticism of this and other ablative techniques is the associated lack of histologic confirmation of complete tumor ablation. Long-term, diligently performed studies that provide detailed, meticulous, sequential 5-year radiologic and histologic data are necessary to confirm lasting efficacy. In addition, these data must be compared with those related to partial nephrectomy, which remains the reference standard.