Using single-crystal NMR, we have measured the full chemical shielding tensor of the Hg-2(2+) ion in mercurous nitrate dihydrate, the first tenser determination of a metallic species involved in a metal-metal bond. The tenser is almost axially symmetric; its unique element is directed approximately along the long axis of the diaquomercurous ion, but it lies closer to the ligand metal axis than the metal-metal bond. The shielding anisotropy of mercury is, as would be expected for a linear mercury compound, quite large (3203 ppm).