Treatment of BiX₃ (X = Cl or Br) with [8]aneSe₂ (1,5-diselenacyclooctane), [16]aneSe₄ (1,5,9,13-tetraselenacyclohexadecane), [24]aneSe₆ (1,5,9,13,17,21-hexaselenacyclotetracosane) yielded species of formula [BiX₃(L)] in moderate to high yield as intensely coloured powdered solids. The crystal structures of [BiCl₃([8]aneSe₂)] and [BiBr₃([16]aneSe₄)] each reveal infinite one-dimensional ladder structures derived from almost planar Bi₂X₆ dimer units linked by μ-bridging cyclic selenoethers. Each Bi is co-ordinated to a Se₂X₄ donor set, with the Se donor atoms occupying mutually trans co-ordination sites. The selenoether ligands adopt exocyclic arrangements and, in [BiBr₃([16]aneSe₄)], it is two trans Se atoms which co-ordinate to Bi^III, leaving the other two Se atoms non-co-ordinating. The structures of these species are contrasted with related complexes involving acyclic selenoether ligands and with the few structurally characterised bismuth(III) halide complexes with macrocyclic thioether ligands.