A side wall of a printing unit of a sheet-fed rotary printing press is composed of a plurality of in-line printing units in accordance with unit construction principles. The side wall has a torsionally rigid side-wall body formed with a boxlike cross-sectional profile open on one side thereof and has a frame extending somewhat transversely to a plane wherein the side wall is disposed. The frame is formed with at least one recess through which gear wheels of a gear-wheel drive train are at least engageable or possess a kinking and back-springing course, respectively, between an upper structural region and a lower structural region of the side wall, including a removable lid ribbed on an inner side thereof and being disposed on the frame in the lower structural region wherein bearings for printing cylinders are received and at an open side of the boxlike cross-sectional profile for stiffening the frame. The frame is formed with recesses in the lower structural region thereof.