The metastable orange modification of HgI2, described earlier by several authors, was obtained by recrystallization of HgI2 from 2-chloroethanol in the form of square, platelike crystals ranging in color from red-orange to yellow-orange. The x-ray photographs of the yellow-orange crystals indicated one-dimensional disorder along c, whereas the reflections from the red-orange form were sharp. The Friedel symmetry is 4/mmm and the lattice constants are twice those of the red form, i.e., a = 8.776, c = 24.723 Å, c/a≃;2√2. Both the hk0 and hhl reciprocal-net planes are identical with the hk0 plane of the red form and there are many systematic extinctions. The structure was solved from these observations. The structural motif is a Hg4I10 group, consisting of four corner-linked HgI4 tetrahedra in a tetrahedral arrangement. These groups are connected into HgI2 layers which are stacked with I–I contacts in the same way as the HgI4 tetrahedra in the red form. In contrast to the red form, there exist two kinds of stacking, leading to a cubic close packing of the iodine atoms. One results in a four-layer structure (red-orange crystals), the other in a two-layer structure. The disorder of the yellow-orange crystals is caused by an irregular succession of the two kinds of stacking. The intensity of the diffuse scattering arising from the disorder was calculated, and is in qualitative agreement with the observations.