A ladder locking system that secures an extension ladder to an accessory rack mounted to a vehicle to define a secured position is provided. The secured ladder is prevented from moving fore or aft relative to the rack. The secured ladder is also prevented from moving laterally relative to the rack and vehicle by the downwardly directed force and engagement provided by the locking system. The locking system is movable to a released position wherein the ladder is not engaged by the locking system and thus can be removed from the ladder rack by an operator. An intermediate position occurs when the operator actuates the locking system between the secured and released positions depending upon whether the ladder is being readied for securement in the rack or being readied for removal from the rack.