beta-Xylosidases are involved in the breakdown of xylans into xylose and belong to either family 39 or 43 of the glycosyl hydrolases. At present, no structural information is available for any member of these families. beta-Xylosidase from the thermophilic anaerobe Thermoanaerobacterium saccharolyticum, a member of glycosyl hydrolase family 39, has been crystallized at 296 K using the hanging-drop vapour-diffusion method. The crystal diffracts to 2.4 A resolution with synchrotron X-rays and belongs to space group P4(1)2(1)2 (or P4(3)2(1)2), with unit-cell parameters a = b = 92.75, c = 241.37 A. The asymmetric unit contains two monomers of the recombinant enzyme, giving a corresponding V(M) of 2.21 A(3)Da(-1) and a solvent content of 44.3%.