The aim of this study was to investigate the potential and feasibility of ultrasound-guided cryotherapy in breast cancer. Fifteen female patients with 16 breast cancers (mean tumour diameter 21±7.8 mm) were treated. A 3-mm cryo probe was placed in the tumour under ultrasound guidance. Two freeze/thaw cycles with durations of 7–10 min and 5 min, respectively, were performed. The size of the iceballs was measured sonographically in 1-min intervals. The patients underwent surgery within 5 days and the specimens were evaluated histologically. The mean diameter of the iceball was 28±2.7 mm after the second freezing cycle. No severe side effects were observed. Five tumours with a diameter below 16 mm did not show any remaining invasive cancer after treatment. Two of these had ductal carcinoma in situ (DCIS) in the surrounding tissue. In 11 patients cryotherapy of tumours reaching diameters of 23 mm or more resulted in incomplete necrosis. This study shows that the invasive components of small tumours can be treated using cryotherapy. Remnant DCIS components which may not be detected preinterventionally represent a challenging problem for complete ablation. In tumours larger than 15 mm two or more cryo probes should be used to achieve larger iceballs.