The invention concerns an HF-surgery device for cutting and/or coagulating biological tissue and a method for same, which in operation monitors the patient skin contact of a connected neutral electrode having at least two separate contact surfaces. The HF-surgery device includes at least one parallel resonant circuit arranged in a patient circuit, at least one measurement energy source arranged in a measurement circuit galvanically separated from the patient circuit for producing a measurement voltage/current acting between the contact surfaces of the neutral electrode, and at least one measuring and computing unit which in operation determines by means of the measurement voltage/current a tissue impedance which is representative of the patient skin contact and which acts between the contact surfaces. An HF-current flows in the patient circuit which is closed in the cutting or coagulation operation and the measurement voltage which is independent of the HF-current can be produced in the measurement circuit. To provide an improved HF-surgery device it is provided according to the invention that the frequency of the measurement voltage source is substantially equal to a resonance frequency of the parallel resonant circuit.
