Crystals of methyl(pyridine)mercury(II) nitrate are orthorhombic and belong to the space group P nma, with a 13.230(3), b 6.538(1), c 9.808(5) Ǻ and Z 4. The diffractometer data, measured with Mo Kα radiation, have been refined to an R index of 0.062 for the 857 observed terms. The crystals are composed of [MeHg(py)]+ cations and uncoordinated nitrate anions. The C-Hg-N moiety is linear, 179.7(6)°, and the N-Hg and C-Hg bonds have lengths of 2.12(2) and 2.04(3) Ǻ respectively.