Abstract: A lightweight collapsible ladder which may be secured to a structure. The ladder includes two parallel uprights which are connected to one another by a plurality of pivotally mounted rungs, and is movable from a closed position in which the uprights abut one another to an open position in which the uprights are apart and the rungs are horizontal. Support devices are provided for supporting the ladder in its open position. A locking device is mounted on the ladder for holding the ladder in its closed position. The rungs are arranged in two adjacent vertical planes, every other rung located in one of the vertical planes and alternate rungs positioned in the other vertical plane.