A collapsible support structure for a folding sled. The support structure, in an erect position, has two vertical members interconnected at their bottoms by a collapsible, preferably horizontal, member. Each end of the horizontal member is also pivotally connected to the other vertical member by a diagonal support member that extends between each end of the horizontal member and an upper portion of the opposite vertical member. When the structure is erect, the diagonal support members form an "X". Stiffening members, which are preferably generally vertical, are spaced from the vertical members and extend between the horizontal member and the diagonal support members. Both the horizontal member and the diagonal support members are formed of a plurality of pivotally interconnected links, at least one of which is modified to maintain the links in a desired angular position when the support structure is erected. A diagonal brace member interconnects each of the runners with the vertical support members not pivotally connected thereto. Collapse of the support structure moves the runners and the vertical members towards each other to reduce the width of the structure.