A surgical instrument (1), in particular an endoscopic surgical instrument, comprises an elongate shaft (10), a surgical tool (2) arranged at a distal end of the shaft (10) for conducting surgical manipulations and a handle arranged at a proximal end of the shaft (10) for actuating the surgical tool (2), the shaft (10) comprising an elongate shaft tube and an elongate actuation rod (61) arranged movably within the shaft tube, the tool (2) and the handle both being connected to the shaft tube and the actuating rod (61) such that the tool (2) can be actuated by the handle through a motion of the actuating rod (61) relative to the shaft tube. The shaft tube comprises an elongate outer shaft tube (14) and an elongate inner shaft tube (15) that is at least partly arranged within the outer shaft tube (14), the outer shaft tube (14) being displaceable in a longitudinal direction with respect to the inner shaft tube (15) and being lockable with respect to the inner shaft tube (15) in a multiplicity of longitudinal positions, and the actuation rod (61) comprises an elongate actuation rod tube (57) and an elongate actuation rod core (58) at least partly arranged within the actuation rod tube (57), the actuation rod tube (57) being displaceable in a longitudinal direction relative to the actuation rod core (58) and being lockable with respect to the actuation rod core (58) in a multiplicity of longitudinal positions.
