Although 6-azido-6-de-oxy-l-galactose in aqueous solution is in equilibrium between the open-chain, furan-ose and pyran-ose forms, it crystallizes solely as 6-azido-6-de-oxy-α-l-galactopyran-ose monohydrate, C(6)H(11)N(3)O(5)·H(2)O, with the six-membered ring adopting a chair conformation. The structure exists as hydrogen-bonded chains, with each mol-ecule acting as a donor and acceptor of five hydrogen bonds. There are no unusual crystal packing features and the absolute configuration was determined from the use of 1-azido-1-de-oxy-d-galactitol as the starting material.