The present structural revision of the title compound, tetracadmium tetrasulfite hexahydrate, [Cd₄(SO₃)₄(H₂O)₅]·H₂O, is a low-temperature upgrade (T = 100 K and R = 0.017) of the original room-temperature structure reported by Kiers & Vos [Cryst. Struct. Commun. (1978). 7, 399-403; T = 293 K and R = 0.080). The compound is a three-dimensional polymer with four independent cadmium centres, four sulfite anions and six water molecules, five of them coordinated to two cadmium centres and the remaining one an unbound solvent molecule which completes the asymmetric unit. There are two types of cadmium environment: CdO₈ (through four chelating sulfite ligands) and CdO₆ (by way of six monocoordinated ligands). The former groups form planar arrays [parallel to (001) and separated by half a unit cell translation along c], made up of chains running along [110] and [110], respectively. These chains are, in turn, interconnected both in an intraplanar as well as in an interplanar fashion by the latter CdO₆ polyhedra into a tight three-dimensional framework. There is, in addition, an extensive network of hydrogen bonds, in which all 12 water H atoms act as donors and eight O atoms from all four sulfite groups and two water molecules act as acceptors.