Abstract: A drill guide apparatus for enabling the accurate drilling of holes in a door for the installation of a door handle assembly or lock comprises a generally U-shaped member sized to fit around the edge of a conventional door into which holes are to be drilled for the installation of the door handle assembly or lock. A C-type clamp is included for rigidly clamping the U-shaped member to the edge of said door in the region to be drilled. A drill bushing is installed through a region of the U-shaped member in a location enabling, when the apparatus is clamped to the edge of the door, the guiding a drill for drilling a hole into the edge of the door. A plurality of side plates is provided, each of which has a plurality of drill guide apertures or bushings arranged in relative locations for guiding the drilling of holes through the door for the installation of a particular type of door handle assembly or lock.