A stand-up type wheelchair for handicapped and sick people comprises a chassis (2) supporting an articulated structure (12) which includes a seat, a foot-rest, a chair-back, and two symmetrical lateral articulated systems. Each system includes a first deformable polygon contributing to the support of the seat, a second deformable polygon, contributing to the support of the foot-rest, a chair-back quadrilateral (four-bar linkage) (35) articulated on the first quadrilateral, and a manoeuvring assembly (40), which includes a first lever (41), a second lever (43), and a manoeuvring handle (49). The manoeuvring handle (49) is articulated firstly on the second lever (43) and/or the first lever (41), and secondly on the first quadrilateral by means of a connecting-rod (55) whose first extremity is connected by a pivot to the first quadrilateral and whose second extremity is connected by a pivot (58) to the manoeuvring handle (49).