The one-dimensional chain catena-poly[[aqua(2,2':6',2"-terpyridyl-kappa(3)N)nickel(II)]-mu-cyano-kappa(2)N:C-[bis(cyano-kappaC)nickelate(II)]-mu-cyano-kappa(2)C:N], [Ni(terpy)(H(2)O)]-trans-[Ni-mu-(CN)(2)-(CN)(2)](n) or [Ni(2)(CN)(4)(C(15)H(11)N(3))(H(2)O)], consists of infinite linear chains along the crystallographic [10-1] direction. The chains are composed of two distinct types of nickel ions, paramagnetic octahedral [Ni(terpy)(H(2)O)](2+) cations (with twofold crystallographic symmetry) and diamagnetic planar [Ni(CN)(4)](2-) anions (with the Ni atom on an inversion center). The [Ni(CN)(4)](2-) units act as bidentate ligands bridging through two trans cyano groups thus giving rise to a new example of a trans-trans chain among planar tetracyanonickelate complexes. The coordination geometry of the planar nickel unit is typical of slightly distorted octahedral nickel(II) complexes, but for the [Ni(CN)(4)](2-) units, the geometry deviates from a planar configuration due to steric interactions with the terpyridine ligands.