Trans-[Ir(pyridine)4Cl2]Cl. 6H2O exists in at least two forms. A high temperature form, crystallized from water at room temperature, is disordered in the solid state. A low temperature form, crystallized from aqueous solution at 2°. has been structurally characterized using x-ray crystallographic methods. It is monoclinic, space group P21/c, a=12.595(2), b=10.498(3), c=21.243(5)Å, β=98.26(2)°, Z=4. The structure was refined to R=0.034, for 3998 reflexions for which I > 3σ(I). The cation has regular octahedral geometry with the Ir-Cl bond lengths equal to 2.35 and the Ir-N bond lengths equal to 2.06 Å. The water molecules, together with the chloride anion lie in hydrogen-bonded sheets at 0.5a.