Abstract: A method and device for hyperthermic treatment of tumors. At least two electrodes connected to an RF source of energy are brought into contact with the patient's body for transmission of RF energy to the tumor area. One of the electrodes constitutes a treatment electrode system, shaped with an external surface the same size as the tumor area and intended to be applied therein, and the other electrode constitutes an indifferent electrode, considerably larger in area, intended to be in external contact with the skin of the body. The treatment device comprises a generator with low impedance, low generator voltage and greatest possible output.