The as-precipitated sulfate-intercalated layered double hydroxide of Zn and Al crystallizes in the structure of the 3R(1) polytype. On hydrothermal treatment, this 3R(1) polytype transforms into the somewhat rare 3H and 3R(2) polytypes at different temperatures. Observation of the 3R(2) polytype distinct from the 3R(1) polytype is evidence for the lack of cation ordering in the [Zn-Al-SO4] system. The layered double hydroxide of Zn and Cr (polytype, 1H) on hydrothermal treatment in mother liquor yields a cation ordered phase also having the structure of the 1H polytype. Direct evidence of cation ordering is found by the appearance of weak supercell reflections corresponding to a = root 3 x a(o) (a(o) is the a parameter of the cation disordered phase). The same precursor under other conditions yields the cation disordered 3R(1) polytype. In this work, the structures of both the cation-ordered and the cation-disordered phases with similar states of hydration are refined and compared.