A combined seat/stair arrangement for a multi-deck vehicle, in particular a multi-deck aircraft or spacecraft, include a foldable passenger seat; a stair which is designed to connect an upper deck to a lower deck via a stair hatch and at least one floor flap which movable between a use position of the stair with the stair hatch open and a use position of the foldable passenger seat with the stair hatch closed, wherein, in the use position of the foldable passenger seat, the at least one floor flap closes at least a partial region of the stair hatch, and wherein the floor flap is designed with a seat attachment, to which the foldable passenger seat is attached.