Tobacco ringspot virus, a plant virus that is believed to fill an apparent niche in the evolution of picornavirus-like capsids, has been crystallized by vapor diffusion with potassium phosphate and polyethylene glycol buffered at pH 6.5 in a new crystal form. The monoclinic crystals belong to the space group C2 with unit-cell dimensions of a = 407.1, b = 399.7, c = 285.9 A and beta = 129.1 degrees and diffract synchrotron radiation to 3.3 A. One half of a virus particle constitutes the crystallographic asymmetric unit. The orientation of the virus particle in the unit cell was determined by the rotation function analysis of a partial data set that has been collected at CHESS using image plates. Development of a suitable phasing model for the high-resolution structure determination of TRSV with the real-space molecular replacement technique is now under way.