Two iodopalladates of the same empirical formula with palladium in different oxidation states were synthesized from aqueous HI solution. Their crystal structures were characterized by single-crystal X-ray analysis, and the effect of hydrostatic pressure on the structural properties has been investigated. Dicesium hexaiodopalladate(IV), Cs2PdI6, crystallizes in a cubic system, space group Fm (3) over bar m, with a = 11.332(1) Angstrom and Z = 4, and is isotypic to K2PtCl6. The second compound, dicesium tetraiodopalladate(II) diiodine, Cs2PdI4. I-2, shows tetragonal symmetry with space group I4/mmm, a = 8.987(1) Angstrom, c = 9.240(1) Angstrom, and Z = 2. The crystal structure can be described in resemblance to the (Cs2AuAuCl6)-Au-I-Cl-III type. Structural relationships and chemical and structural transformation between both compounds will be discussed. DTA measurements at ambient pressure showed liberation of I-2 and decomposition of the compounds. Cs2PdI4. I-2 represents an excellent example for studying a solid-state electron-transfer reaction. The redox reaction to Cs2PdI6 can be demonstrated by performing pressure-dependent X-ray studies.