The asymmetric unit of the three-dimensional Cu(II)-W(IV) polymeric assembly [Cu(en)(2)][Cu(en)][W(CN)(8)].4H(2)O](n) (en is ethylenediamine, C(2)H(8)N(2)) or [Cu(2)W(CN)(8)(C(2)H(8)N(2))(3)].4H(2)O](n), which can be named as polymeric bis(ethylenediamine)copper(II) (ethylenediamine)copper(II) octacyanotungstate(IV) tetrahydrate or penta-micro-cyano-tricyanotris(ethylenediamine)dicopper(II)tungsten(IV) tetrahydrate, consists of two half [Cu(en)(2)](2+) cations (Cu(2+) on inversion centres), a [Cu(en)](2+) cation and a [W(CN)(8)](4-) ion, together with four water molecules. The latter Cu(II) site is coordinated by five N atoms from an en ligand and by three cyanides in a distorted square-pyramidal geometry. The Cu(II) atoms of the two [Cu(en)(2)](2+) cations reside in an elongated octahedral coordination environment, and one of them is localized at a centre of inversion. The W atom is coordinated by eight cyano groups in an irregular square antiprism. Five of these act as bridging units connecting the W and the three Cu atoms, to form an infinite three-dimensional porous network containing a zigzag ladder structure.