A study of tungsten trioxide (WO3) by differential thermal analysis and x-ray diffraction at temperatures up to 980°C showed a new tetragonal form to exist at temperatures of 740°C and higher. This form has a distorted ReO3 structure. There are two molecules in a unit cell of dimensions a0=5.25A, c0=3.91A. All atoms lie in the 2- or 4-fold special positions of the space group P4/nmm. The tungsten atoms are alternately displaced in opposite directions from the center of charge of the oxygen atoms so as to resemble the antiferroelectric structure proposed by Kittel.