The region spanning the tetrameric coiled-coil domain and the interspecies-variable virulence-determining region of the cytoplasmic tail of rotaviral nonstructural protein NSP4 has been crystallized. The crystals belong to space group I222, with unit-cell parameters a = 30.70, b = 38.07, c = 181.62 Å, and contain two molecules in the asymmetric unit. Diffraction data have been collected utilizing a MAR imaging plate to a resolution of 2.2 Å. The tetramer is generated by the crystallographic dyad along the c axis. © 2004 International Union of Crystallography.