Abstract: A sealing element for a cylinder-and-piston unit, especially a dust boot of a disc-brake actuating unit, includes an annular deformable portion of an elastically deformable material, and an annular connecting portion of a resilient material which is permanently sealingly connected to the inner region of the deformable portion and mounts the same on a protruding annular portion of the piston which extends out of the cylinder, by clampingly engaging such protruding portion. The connecting portion is substantially U-shaped in axial section and includes an outer ring, an inner ring and an interconnecting web extending between the outer and inner rings. The inner ring converges in the direction of introduction thereof into the annular protruding portion of the piston and carries oppositely and outwardly oriented lugs which engage behind an internal bead of the protruding portion of the piston. A brake shoe has a clip with several prongs which engage behind the inner ring of the connecting portion.