The syntheses of bisdithiocarbamates from diamines and CS2 are described, and possible complications in these reactions explained. Ethylenebisdithiocarbamate was prepared from ethylenediamine and CS2 in basic solution, but the same reaction using o-phenylenediamine led to a cyclization product, o-phenyleneimidazolidine-2-thione or benzimidazolidine-2-thione. In these reactions, if slightly insufficient amounts of CS2 are used, bisdithiocarbamates will not be formed; instead, the cyclization reactions will occur, leading to the formation of thiones. Crystallographic studies were carried out for disodium ethylenebisdithiocarbamate and imidazolidine-2-thione or ethylenethiourea. The hexahydrate crystals of the former, Na2[S2CNHCH2CH2NHCS2]•6H2O, F.W. 364.42, are triclinic with a = 5.766(1), b = 7.212(1), c = 10.074(1) Å, α = 88.53(1), β = 98.41(1), γ = 105.50(1)°, V = 399.3(1) Å3, and Z = 1. The structure was determined from 2259 unique reflections, (2θ[Mo-Kα] < 65°) to an R factor of 0.022. The bisdithiocarbamate ion has a center of symmetry between the two CH2 groups, and therefore the two NCS22− groups are separated as far apart as possible. Each Na+ ion is octahedrally surrounded by five water molecules with Na … O distances ranging from 2.373 to 2.446 Å, and a sulphur atom of the thiocarbamate group with Na … S = 3.060 Å. The two C—S bonds of the CS2− group are 1.710(1) and 1.727(1) Å, and [Formula: see text]. Crystals of imidazolidine-2-thione, (CH2NH)2CS, are monoclinic, with a = 5.800(1), b = 14.516(3), c = 5.780(1) Å, β = 101.33(2)°, V = 477.2(2) Å3, and Z = 4. This structure, first determined thirty years ago, has been refined by full-matrix least-squares to R = 0.031, using 975 new Mo-Kα data.