A medical instrument comprises a guide tube (10) that can be inserted into a duct in a patient's body. An elastically flexible cannula is displaceable within an inner axial guide channel of the guide tube (10), and its distal tip (52) can emerge through an opening arranged laterally on the circumference of the guide tube (10), thus emerging at an angle bent away from the axis of the guide tube (10). The proximal end of the guide tube (10) is received in a grip part (22) such as to be rotatable about its longitudinal axis.