The invention relates to a medical instrument comprising a medical tool intended, while a medical act is being performed, to be maintained by a user and/or by a robot and the position of which is intended to be determined by a tracking system, and comprising a display system having a visual control screen, a connection element connecting the display system to the tool and maintaining the minimum distance between the visual control screen and the tool under 15 centimeters and being capable of orienting the visual control screen with respect to the tool, means for transmitting to the display system data to be displayed on the visual control screen which depend on the determined position of the tool, means for supplying the display system, and a sterile enclosure containing the visual control screen, the transmission means, and the supply means.