This paper describes the development of a cryo-device for the treatment of tumors. The probes are intended to form an iceball inside of an organ, e.g. the liver, to destroy degenerated cells. After successful preliminary tests and the development and construction of several probes, the emphasis is now being placed on the realization of a complete device prototype which will enable clinical studies to be carried out. Important for the functionality of the device is an integrated temperature sensor inside the probes. The device may also be used for cryo-analgesic purposes in pain treatment.