The backrest of a chair comprises a frame, a backrest support and a neck support. A membrane is clipped into the frame, and the backrest support is articulated on a tilting mechanism. The frame comprises two side parts and two cross-pieces, the lower cross-piece lying at the height of the user's lumbar vertebra. The frame and the backrest support are interconnected in one piece. The component created as a result is advantageously a plastic injection molding produced by the gas injection technique (GIT) and the plastic is a glass-fiber-reinforced polyarylamide. This overall structure of the backrest provides a high level of sitting comfort by elastic support of the back in all major regions and directions of movement, but at the same time also considerably reduces production, transport and assembly complexity and has an aesthetically impressive, distinctive form.