Lumazine synthase from Brucella abortus was overexpressed in Escherichia coli, refolded, and purified to apparent homogeneity. Crystals of lumazine synthase were grown by the hanging drop vapor diffusion method using polyethylene glycol 8000 or ammonium sulfate as precipitants. They belong to the trigonal space group P321 with cell parameters a = b = 132.00 Angstrom, c = 167.25 Angstrom. A complete diffraction data set to 3.7 Angstrom resolution has been collected using synchrotron radiation. Preliminary analysis of the quaternary structure of this protein by means of a self-rotation function calculated with the diffraction data clearly indicates 532 symmetry compatible with the presence of an icosahedral lumazine synthase particle.