Abstract: A surgical drilling guide for guiding a drilling tool, measuring its penetration depth, and protecting surrounding tissue. The guide has a sleeve and a plunger that telescopes within the sleeve. The plunger and the sleeve have axial bores adapted to slidably receive a portion of the tool that protrudes beyond a drill chuck. The extended length of the drilling guide is substantially as long as the length of the protruding portion of the tool, and a maximum extended length of the guide is preferably as long as the protruding portion. As the tool in drilled into a workpiece, the chuck collapses the drilling guide. Gradations on the side of the guide indicate workpiece-penetration depth.