Abstract: A locking device for sliding windows and doors, including a removal-preventing bar, wherein the window is freely slidable within a track formed in the lower frame portion of a window casement, the locking device comprising a main body having a lower groove to receive a flanged wall of the track, and the body being secured thereto by an adjustable screw, the body further including a lateral-extending boss member for direct engagement with the sliding window to limit lateral movement thereof. The removal-preventing bar is secured in the main body and projects longitudinally therefrom adjacent the lower frame portion of the window and above the track of the casement, thereby preventing the window from being removed from the casement frame structure.