A medical device equipped for switching the device on and off carries out at least one safety-relevant function in the operating state, using at least one operating parameter with a set target value. In order to ensure a reliable function of the device and not disturb a medical treatment, the device performs a first self-diagnosis following switch-on and before reaching an operating state and performs a second self-diagnosis following switch-off and before terminating the operating state, during which self-diagnoses the same operating parameter of the device is checked in each case for deviation from the target value. The technology also relates to a corresponding method for operating a medical device.