An automatic detection of surgical instruments with respect to a type and a location thereof is provided with a detection system, which includes at least two surgical instruments, which each include at least one cavity extending along a longitudinal axis of the instrument and a proximal entry region to the cavity. An angle of the proximal entry region in relation to the longitudinal extension of the cavity is different in the two instruments. A sensor unit includes two electromagnetic sensors and is insertable into the cavity. One of the sensors extends axially in the cavity, and the other sensor is arranged in the entry region. A field generator generates an electromagnetic field. An analysis unit analyzes signals transmitted by the sensors to the analysis unit in accordance with the location thereof in the field of the field generator.