Key indicators: single-crystal X-ray study; T = 150 K; mean (C-C) = 0.003 Å; R factor = 0.032; wR factor = 0.073; data-to-parameter ratio = 10.1.The relative configuration of the title compound, C 11 H 18 O 6 , was firmly established by X-ray crystallographic analysis. The absolute configuration was determined by the use of 2-Cmethyl-d-ribono-1,4-lactone as the starting material. The structure exists as a hydrogen-bonded network, with each molecule acting as a donor and acceptor for two hydrogen bonds.