The cooling capacity of modern cryoprobes is sufficient to freeze, within 15 minutes, a tumor of approximately 2 cm in diameter to temperatures below -50°C when the probe is located exactly in the center of the tumor. According to our experience, a controlled placement of cryoprobes into small tumors is often technically difficult and an eccentric placement may occur. In addition blood vessels, in the vicinity of the tissue region to be frozen, may reduce the spatial extension of the region cooled to -50°C or less. We have investigated the effect of such factors on the safe cryo-destruction of small tumors by using a computer program by which the temporal and the spatial distribution of the temperatures were calculated and displayed as color-coded isotherms. Such calculations indicate that for the treatment of metastases in the range of 2 cm or for the treatment of multiple metastases, 3 cryoprobes placed outside the tumor should give superior results compared to freezing with I or 2 cryoprobes.