Abstract: A security bar for securely holding in a closed position a horizontally sliding door, such as a so-called patio door, for example, or a horizontally or vertically sliding window. The security bar of the invention consists of a massive metallic or plastic bar member, preferably square or rectangular in cross-section, pivotally supported at one end by means of a bracket from an inoperative position to an operative position wherein the free end of the bar member is supported by a clip with the longitudinal axis of the bar member substantially orthogonal to the rear edge of the frame of the sliding door or window and to a fixed structural surface such as the door or window jamb.