A self-adjusting closing system for window or door frames with a fixed frame (7) and at least one moving shutter (6) hinged thereto, comprising: an abutment (5) blocked to fixed frame (7) and formed by a surface (5a) parallel to a surface (7b) of the section bar of fixed frame (7) with a rounded edge (5b) and a protrusion (5c) having a surface (5d) perpendicular to surface (5a); and a cursor able to slide within a channel (6c) of the moving shutter (6) to said perpendicular surface (5d) of abutment (5).
Said perpendicular surface (5d) of protrusion (5c) occupies a portion of the whole length of abutment (5), and said cursor includes a pull-out member or button (2) able to move to a perpendicular direction to the movement of the cursor, said pull-out member or button (2) being able to engage with said protrusion (5c) of abutment (5).