Abstract: An extendible and tiltable shim is provided having a hingeably connected leg that is extendable. The leg can extend to adjust the height and the angle of the shim. The shim is mounted to a structure member and abuts to a frame member. The structure member can comprise a rough opening in a wall. The frame member can comprise a door jamb or a window jamb. The method of the invention includes an initial step of attaching the bottom plate of the shim to a structure, extending the leg to contact the frame member, and adjusting the extension of the leg to center and plumb the frame member. The shim accurately and reliably adjusts a door jamb or window jamb within a rough opening in a wall for proper alignment. The shim tilts at an angle and offsets to accommodate crooked and misaligned wall structure. The shim can easily retrofit to a standard door jamb or a window frame for the purpose of aiding in the square alignment of the door jamb or window jamb within a rough opening in wall structure.