The crystal structure of mercurous iodide, Hg(2)I(2), has been determined previously from X-ray powder diffraction data [Havighurst (1926 ▶). J. Am. Chem. Soc.48, 2113-2125]. The results of the current redetermination based on single-crystal X-ray diffraction data provide more precise geometrical data and also anisotropic displacement parameters for the Hg and I atoms, which are both situated on positions with site-symmetry 4mm. The structure consists of linear dimers I-Hg-Hg-I extending along the c axis with an Hg-Hg distance of 2.5903 (13) Å. The overall coordination sphere of the Hg(+) atom is a considerably distorted octa-hedron. The crystal specimen under investigation was twinned by non-merohedry with a refined twin domain fraction of 0.853 (14):0.147 (14).