Ammonium dithiocarbamate, H₂NCS₂NH₄, decomposes easily but the anion forms a stable mercury(II) complex, the crystals of which are orthorhombic with a = 7.851(3), b = 17.565(7), c = 12.051(3) Å, and space group Pbca. The structure was solved by the Patterson method and refined by the full-matrix least-squares method to an R of 0.038 for 781 reflections. The structure consists of layers of two-dimensional polymeric networks. The dimeric subunits in the layer containing two each of mutually connected Hg atoms and dithiocarbamates are further linked by other bridging dithiocarbamates forming a sheet-like structure. Each Hg atom bonds to four S atoms from four separate dithiocarbamates with Hg—S distances of 2.499(4), 2.508(4), 2.533(4), and 2.629(4) Å. The ir bands observed were: ν(NH₂), 3320, 3220, 3125; δ(NH₂), 1600; ν(C—N), 1395; ρ_r(NH₂), 1172; and v(C—S), 840 cm⁻¹. The mass spectrum of this polymeric compound gave peaks corresponding to Hg, S₂, CNH₂, HNCS, S, CS₂, S₅, S₄, S₃, and S₈ in the order of their intensities.