INTRODUCTION Percutaneous ablation in the kidney is now performed as a standard therapeutic nephron-sparing option in patients who are poor candidates for resection. Its increasing use has been largely prompted by the rising incidental detection of renal cell carcinomas with cross-sectional imaging and the need to preserve renal function in patients with comorbid conditions, multiple renal cell carcinomas, and/or heritable renal cancer syndromes. To date, clinical studies indicate that cryoablation is an effective therapy with acceptable short- to intermediate-term outcomes and with a low risk in the appropriate setting. This article focuses on the efficiency of contrast enhanced ultrasound scan (CEUS) as compared to contrast enhanced magnetic resonance imaging (MRI) during the follow-up after cryoablation of small renal tumors. MATERIAL & METHODS In our Department, percutaneous or laparoscopic assisted cryoablation is offered in the treatment of small renal masses. Between January 2009 and January 2013, 25 patients (pts) were treated with laparoscopic assisted cryoablation or percutaneous cryoablation for renal tumors <3.5 cm in pts unfit for surgery. All pts had severe comorbidities (ASA score 3). Transperitoneal laparoscopic approach was performed in 11 pts, extraperitoneal approach in 3 pts, percutaneous technique was performed in 11 patients. "Tru-cut biopsy" of the renal mass was always performed before cryoablation. The SeedNet system (Galil Medical, Arden Hills, MN) was used in 12/25 pts; the Precise system (Galil Medical, Arden Hills, MN) was used in 13/25 pts. In all cases, IceRod needles were used. Real-time ultrasound guidance was used to localize the tumour and to monitor the progression of "iceball". A double "freeze-thaw cycle" was used. All pts had MRI and CEUS before cryoablation and the follow-up consisted in CEUS/MRI every 3 months during the first year and every 6 months thereafter. RESULTS The mean age of the 25 pts was 67.7 years (range 56-79); 5 pts were females and 20 were males. The mean tumor size was 2.8 cm (range 1.5-3.5). No patient required conversion to open procedure. 19 tumors were located at the lower pole, 4 were interpolar and 2 tumors were located at the upper pole. There were no intraoperative complications. The mean hospital stay was 4 days (range 1-7). Two pts required a blood transfusion; there was no statistically significant difference between preoperative and postoperative serum creatinine levels. The biopsy showed RCC in all cases. In 24/25 patients both CEUS and MRI showed no enhancement. In 1/25 pts, during the follow-up, CEUS and MRI showed a well visible recurrence at the perfusion study. It was histologically confirmed. The final results of CEUS and MRI were concordant in all pts. CONCLUSIONS CEUS is effective during the follow-up of renal tumor cryoablation. It could be an alternative technique to standard CT and MRI, with some advantages: low cost, short time consuming procedure, no radiation exposure, reduced amount of contrast agent (1-2 mL) and rare adverse reactions.