The crystal structure of perdeuterodimethyl sulfoxide, (CD3)2SO, has been refined at 2 and 100 K, and characterized as a function of temperature up to 275 K against high-resolution neutron powder diffraction data. The structure determined previously by Thomas, Shoemaker & Eriks [Acta Cryst. (1966), 21, 12-20] (T=278 K) is shown to remain down to 2 K. At 2 K, the S-O bond distance is 1.495 (2) A. The fact that the molecule is distorted from ideal Cs point symmetry may be explained by the short D...O contacts of the respective methyl groups.