Abstract: A sliding door security insert assembly installable into an opening made when one sliding door mounted for lateral movement within a door frame is partially opened to define the opening between one door jamb and a facing sliding door stile. A substantially rectangular insert frame includes a lower transverse member adapted to be supported on the lower track while said upper transverse member is adapted to be positioned into the upper track for lateral sliding movement only. An elongated locking shim is positionable between the upper transverse member and the upper track prevents insert frame removal. Offset locking pins attached to one insert frame stile are adapted to be inserted into a mating hole formed into the facing sliding door stile and visa versa whereby the insert frame and the sliding door are connectable together. Full adjustability in height and mating thickness with the existing sliding door edge is also provided.