The invention relates to a straddling dowel comprising a dowel sleeve and a straddling screw (10). According to the invention a rear flank (20) of the screw thread (18) of the straddling screw (10) is oriented, in the direction of screwing, at a flat angle of approximately 9° in relation to the direction of the axis of the straddling screw (10) and the screw thread (18) is formed with a large thread pitch. When the straddling screw (10) is impinged upon in the direction of extraction, the rear flank (20) acts in the manner of straddling cone-shaped elements which are arranged axially behind each other and the sleeve of the dowel is expanded. The straddling dowel is post-expanded when the bore hole is widened. In order to prevent the straddling screw (10) from rotating out of the sleeve of the dowel, anti-rotation flanks (26) which are oriented both radially and in a longitudinal direction are provided on the screw thread (18), said flanks pressing into the dowel sleeve during expansion and thereby preventing the straddling screw (10) from rotating out of the dowel sleeve.