IREM-1 is an inhibitory receptor involved in the functional regulation of myeloid cells. The expression, in vitro folding, purification, crystallization and X-ray data collection of the Ig-V like domain of IREM-1 are reported. X-ray data were collected from a microcrystal (300 x 10 x 10 microm) at 100 K and a diffraction pattern was obtained to 2.6 A resolution on microfocus beamline ID23-2 at the ESRF. The crystal belongs to space group P3(1)21, with unit-cell parameters a = b = 54.23, c = 72.02 A, alpha = gamma = 90, beta = 120 degrees. Assuming the presence of one molecule per asymmetric unit, V(M) (the Matthews coefficient) was calculated to be 1.96 A3 Da(-1) and the solvent content was estimated to be 37.27%. Determination of the IREM-1 structure will provide insights into its structural requirements for ligand discrimination and binding.