The crystal and molecular structure of (SPMe(2))(2)NH and its cobalt(II) complex were determined by X-ray diffraction. In the crystal the molecules of the free acid are associated into polymeric chains through N(1)-H(1’)...S(2a) hydrogen bonds, which results in the non-equivalence of the P=S bond lengths (P(1)-S(1) = 1.939(2), and P(2)-S(2) = 1.962(2) Angstrom) within the molecular unit. The crystal of Co[(SPMe(2))(2)N](2) contains discrete monomeric molecules, exhibiting a spirobicyclic system with a slightly distorted tetrahedral CoS4 core.