The compounds CeB4, ThB4, and UB4 have been shown to crystallize in a new structure, which has been worked out from x-ray diffraction patterns. This structure is designated as the "ThB4-type structure," since that was the compound first observed. These borides were prepared by D.L. Sawyer and L. Brewer of the Lawrence Radiation Laboratory, who heated the metals and boron together in vacuum at about 1500© C. Powder diffraction patterns were obtained of the three compounds. Rotation and Weissenberg patterns were obtained for 110 and 001 axes of a small single crystal of ThB4. The patterns were indexed on tetragonal lattices.