3,3′-Dideoxy-αα-trehalose has been synthesised from the readily available 4,6-O-benzylidene-3-deoxy-α-D-arabino-hexopyranosyl 4,6-O-benzylidene-3-deoxy-α-D-arabino-hexopyranoside by sequential oxidation to the 2,2′-diulose, reduction to the 2,2′-diepimer, and hydrolytic removal of the benzylidene substituents. The dibenzylidene derivative formed by reduction of the diulose was converted into its 2,2′-di-O-methanesulphonate, which underwent a slow SN2 displacement reaction with azide anion to give, with inversion of configuration at C-2 and C-2′, the 2,2′-diazide. Subsequent removal of the benzylidene groups, reduction, and N-acetylation afforded 2-acetamido-2,3-dideoxy-α-D-arabino-hexopyranosyl 2-acetamido-2,3-dideoxy-α-D-arabino-hexopyranoside.