The invention relates to an impression cylinder (1) intended for a sheet-fed machine and having at least one cylinder gap (3) in which sheet grippers (4) are arranged in such a manner that, when closed, they do not project over the envelope of the peripheral area of the impression cylinder (1). The cylinder gap (3) is provided with a cover (7) which can be adjusted by a controlling unit (9, 10, 11, 12) and is subsequently always in its closed position in which it completely covers the cylinder gap (3), when said gap (3) passes through the nip. Consequently, the impression cylinder rolls with a continuous, closed peripheral area on the cylinder printing the image. In the zones where the sheet is transferred to and from the impression cylinder (1), the cover (7) (preferably controlled by a fixed cam (11) while the cylinder is rotating) is opened to such an extent that the sheet grippers (4) can move into the open position thereof to pick up or release a sheet.