The title compound, catena-poly[[mu-cyano-1:2kappa(2)C:N-dicyano-1kappa(2)C-trans-bis[N-(2-hydroxyethyl)ethane-1,2-diamine-2kappa(2)N,N']cadmium(II)nickel(II)]-mu-cyano-1:2'kappa(2)C:N], [CdNi(CN)(4)(C(4)H(12)N(2)O)(2)], consists of alternating square-planar Ni(CN)(4) fragments, formally dianionic, and Cd(hydet-en)(2) moieties [hydet-en is N-(2-hydroxyethyl)ethylenediamine], with the two bridging cyanide ligands in a mutually trans disposition at the Ni atom and cis at the Cd atom. The resulting one-dimensional zigzag chain structure has the Ni atom on an inversion center, while the distorted octahedron centered on the Cd atom lies on a twofold axis. The polymer chains are connected into undulating sheets by weak interchain N-H...N, N-H...O and O-H...N hydrogen bonds, which are also present between successive sheets.