Abstract: A synchronous rotary cross-cutter is disclosed with two oppositely rotated, axially parallel cutting rotors that support cooperating, helically extending knife blades with cutting edges situated in a cylindrical envelope. The axes of these cutting edges run at an angle, corresponding to the inclination of the helix, with respect to the direction of advancement of the material web being cut. To accommodate different cutting lengths without the need for a controllable irregular drive for this purpose, the axial distance of the cutting rotors from the material web is variable and the knives are mounted on a flat blade holder that runs substantially tangentially in the rotor cross section and is slightly flexible. The knife blade holder, supported by a series of individually adjustable supporting elements, can be given a slight flexure with a radial adjustment, so as to assure that the position of the cutting edge of the knife remains within in the cylindrical envelope.