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.Linvention concerne un dispositif chirurgical HF pour sectionner et/ou coaguler un tissu biologique, et un procédé pour celui-ci, qui lors du fonctionnement, surveille le contact avec la peau du patient dune électrode neutre raccordée ayant au moins deux surfaces de contact séparées. Le dispositif chirurgical HF comprend au moins un circuit résonnant en parallèle disposé dans le circuit dun patient, au moins une source dénergie de mesure disposée dans un circuit de mesure séparé galvaniquement du circuit du patient pour produire une tension de mesure/courant agissant entre les surfaces de contact de lélectrode neutre et au moins une unité de mesure et de calcul qui, en fonctionnement, détermine au moyen de la tension de mesure/courant, une impédance
