A wheelchair has two foldable side frames, link members which cross one another and are pivotable about a common horizontal axis so as to fold the side frames, front wheels and rear wheels connected with the side frames, a back rest with upwardly extending back supporting members, a seat with seat supporting members which are movable upwardly and downwardly in dependence upon a folding movement, and a foot support with foot support carrying arms, wherein each side frame is provided with guide receivers for the seat supporting members, and with supports for the link members, and wherein a rear wheel axle block and the front support carrying arms are formed as a one-piece element of synthetic plastic material. Such side frames have a lower weight, but are stable nevertheless, and also result in an improved handling of the wheelchair.