Abstract: A wheelchair has a pair of wheels supporting a frame, a pair of front castors, a seat, and an anti-tipping device on the frame. The anti-tipping device includes an extensible and retractable displacement mechanism including an actuating member manually accessible by a person seated on the seat for displacing a ground engagement member between a forwardly retracted inoperative position, in which the ground engagement member is retracted beneath the seat, and a rearwardly extended operative or deployed position, in which the ground engagement member is extended rearwardly from the frame.