A method for the fabrication of freestanding microstructures in bulk single-crystalline diamond was developed. The method takes advantage of the fact that ion irradiation of diamond followed by thermal annealing induces a phase transformation to amorphous carbon. MeV ion implantation followed by thermal annealing to create a buried sacrificial layer at a well-defined depth was also carried out in the method. Patterned milling with a focused ion beam (FIB) was used to expose defined regions of the sacrificial layer to selective chemical etching. The method has also great potential for the production of microresonators, beams for integration in MEMS with waveguide sensing, and whole classes of high-performance devices.