An electrosurgical system includes an electrosurgical generator 10, for generating radio frequency power, and an electrosurgical instrument 12 including an electrode assembly 18. The electrosurgical instrument 12 is detachably connectible to the generator 10 such that radio frequency power can be conveyed to the electrode assembly 18. The generator includes a counter 51 incremented each time an electrosurgical instrument is connected to the generator 10, and the electrosurgical instrument includes a memory device capable of recording the value of the counter 51 when the electrosurgical instrument is connected to the generator. The system further includes a comparison unit 53 capable of comparing the current value of the counter with the value of the counter stored in the memory device, and generating a signal when the difference between the two values of the counter is greater than a predetermined threshold.
