A neutron powder-diffraction analysis of uranium tribromide has been carried out with the profile-fitting technique and has confirmed that UBr 3 is of the UCl 3 structure type. The final value of R = ∑ i (|I o i − I c i |)/ ∑ i I o i was 0.10, where I o i is one of the 395 background-corrected measured intensities in the pattern. UBr 3 is hexagonal, space group P6 3 m(C 6ith 2) with a = 7.942(2) and c = 4.441(2) Å and Z = 2. The uranium atoms lie in positions 2(d), ± ( 2 3 , 1 3 , 1 4) and the bromine atoms in positions 6(h), ± ( x, y, 1 4 ; −y, x − y, 1 4 ; y − x, x ̄ , 1 4 ) with x = 0.2996(4) and z = 0.3859(4). The configuration around the uranium atom is a tricapped trigonal prism, with U−Br (3×) = 3.145(3) A ̊ (uranium to capping bromine atom) and U−Br (6×) = 3.062(2) A ̊ (uranium to bromine at corner of trigonal prism).