Reaction of mercury(II) diiodide with triphenyl selenophosphorane-Se (1:1 mole ratio) in acetone followed by recrystallisation of the product from chloroform formed crystals of stoichiometry HgI2(Ph3PSe)(1). Compound1 exists as a centrosymmetric homobimetallic dimer, Hg(Μ-I)I(Ph3PSe)2, as monoclinic crystals of space group P21/n. The dimer comprises two Μ2-iodo atoms that form unequal Hg-I bonds 2.8230(10), 3.1135(9) å and two equal terminal Hg-I bonds 2.6524(10) å. The Se atom of Ph3PSe forms terminal Hg-Se bond 2.5914(11)å and thus the geometry about each Hg centre is distorted tetrahedral and the range of tetrahedral bond angles is 92.97(2) to 130.85(3)‡, the largest being that of Se(1)-Hg(1)-I(1) and the shortest, I(2)-Hg(1)-I(2)‡. Hg-Hg and I-I separations of 4.0930(11)å and 4.3097(15)å are more than the sums of their respective van der Waal radii 3.00 å and 4.24 å.