The structure of the tetragonal phase of the A-site-substituted perovskite sodium bismuth titanate, Na(0.5)Bi(0.5)TiO3, has been determined by neutron powder diffraction at 698 K. The structure was refined in space group P4bm with a (= b) = 5.5191 (1), c = 3.9085 (1) A, V= 119.055 (5) A3, Z = 2 and Dx = 5.91 Mg m(-3). The structure exhibits an unusual combination of in-phase (a0a0c+) tilts and antiparallel cation displacements along the polar c axis, which results in a new variant of the perovskite structure.