A laboratory-scale synthesis of UF 4 is presented that utilizes the reduction of UF 6 with sulfur in anhydrous hydrogen fluoride. An excess of sulfur can be removed by vacuum sublimation, yielding pure UF 4 , as shown by powder X-ray diffraction, micro X-ray fluorescence analysis, infrared and Raman spectroscopy, as well as magnetic measurements. Furthermore, a single-crystalline, high-pressure modification of UF 4 was obtained in a multi-anvil press at elevated temperatures. The high-pressure polymorph HP-UF 4 was characterized by means of single-crystal and powder X-ray diffraction, as well as by magnetic measurements, and presents a novel crystal structure type. Quantum-chemical calculations show the HP-modification to be 10 kJ mol −1 per formula unit higher in energy compared to UF 4 .