A ladder mounting and retaining system for use on building parapets utilizes a parapet support member secured to the parapet of a building, a ladder support member for retaining the sides of the lengths of a ladder, and a connecting member in the form of a threaded rod, interconnecting the parapet support member and the ladder support member for maintaining these members at a given distance from each other. The parapet support member is secured in position by locking nuts threaded around the connecting member and the ladder support member is secured over the outboard edge of the parapet by retention members. Ladder supports are adjustable on the ladder support member to accommodate ladders of different widths.