Lanthanum nickel niobium trioxide has been synthesized and its structure refined for the first time. It was found to be a member of the family of technologically important ;double perovskites', crystallizing in the monoclinic space group P2(1)/n. The structure is characterized by a strong orthorhombic pseudosymmetry and a concurrent exhibition of both 1:1 B-cation ordering and a(-)a(-)c(+)-type tilting of the (Ni/Nb)O(6) structural units. Trivalent lanthanum resides on the perovskite A site, which is strongly distorted owing to the tilting of the (Ni/Nb)O(6) sublattice. Ordering of divalent nickel and pentavalent niobium on the B sublattice is described in terms of two twofold special positions (2c and 2d), with nickel taking almost complete occupancy of the 2d site and the 2c position being occupied by a statistical distribution of nickel and niobium.