A three-dimensional X-ray-diffraction analysis of tetra-acetylethane has been carried out. The crystal are orthorhombic, space group Pbcn, with a= 9·18, b= 9·42, c= 11·66 Å, Z= 4. The molecule exists in the dienolic form in the crystal. It has crystallographic symmetry 2 (C2) but, in fact, approximates closely to 2m(D2d), consisting of two substantially planar halves twisted through almost 90° with respect to each other. Each half contains a short and, probably, symmetrical hydrogen bond. The bond lengths and angles are compared with those in a number of metal acetylacetonates, and close similarities are traced.