The C-terminal truncated form of the S-layer protein SbsC from Geobacillus stearothermophilus, rSbsC(31-844), has been crystallized by the vapour-diffusion method using polyethylene glycol 6000 as a precipitating agent. The crystals diffract to 3 A resolution using synchrotron radiation and belong to space group P2(1), with unit-cell parameters a = 57.24, b = 98.91, c = 108.62 A, beta = 94.34 degrees. One molecule is present in the asymmetric unit, which corresponds to a solvent content of 65%. Native and heavy-atom derivative data have been collected. The Pt derivative yielded two high-occupancy sites per molecule.