The structures of orthorhombic (a=5.5686(2)Å, b=9.8946 (2)Å, c=3.19369(12Å) and cubic (a=9.177(3)Å) Cd2SnO4were refined by Rietveld analysis of X-ray powder diffraction patterns. Both of these polymorphs were chemically treated with hydrogen gas mixtures at 400°C, resulting in a colour change from yellow to green. Small structural changes were observed for the orthorhombic material, which underwent a uniform contraction (≈0.02%) of cell size and movement of some oxygen atoms towards the tin atoms. Evidence for loss of structural oxygen was sought, but could not be found above the detection limit of 0.3%. Cubic Cd2SnO4possesses the spinel structure with a large (at least 65%) degree of inversion. Samples prepared with a smaller cell have so far proved unsuitable for Reitveld analysis.