The invention relates to a backrest for supporting the back of a seated person, the backrest comprising mounting means for mounting the backrest on a frame of a seating device comprising: —a first back part for supporting at least a part of the back of the person at a determined angle, which first back part has a stiffness such that during use the part of the back shapes itself substantially to the first back part, and wherein the backrest comprises adjusting means for adjusting the angle and/or the position of the first back part relative to the frame and —a second back part which has a flexibility such that during use the second back part shapes itself substantially continuously to another part of the back of the person. The invention further relates to a method for adjusting such a backrest and a (wheel) chair provided with such a backrest.
