The machining of 3D microstructures in single-crystal artificial diamond is demonstrated with a focused ion beam (FIB)-assisted lift-off technique. A sacrificial buried layer is created with MeV ion implantation, followed by patterning of selected regions with the FIB technique; the sacrificial layer is then selectively etched, leaving 3D free-standing microstructures in the bulk (see Figure). Using this fabrication technique, light waveguiding through a microstructure in single-crystal diamond is demonstrated for the first time.