Methods and apparatuses for temperature modification of a patient, or selected regions thereof, including an induced state of hypothermia. The temperature modification is accomplished using an in-dwelling heat exchange catheter within which a fluid heat exchange medium circulates. A heat exchange cassette is attached to the circulatory conduits of the catheter, the heat exchange cassette being sized to engage a cavity within a control unit. The control unit includes a heater/cooler device for providing heated or cooled fluid to a heat exchanger in thermal communication with the fluid heat exchange medium circulating to the heat exchange catheter, a user input device, and a processor connected to receive input from various sensors around the body and the system. A temperature control scheme for ramping the body temperature up or down without overshoot is provided.