Crystals of the 52 kDa monomeric Escherichia coli cysteinyl-tRNA synthetase complexed with ATP and cysteine have been grown by hanging-drop vapor diffusion from solutions containing ammonium sulfate as the precipitating agent. The crystals form long hexagonal rods in the space group P321 with unit-cell dimensions a = b = 82.3, c = 168.9 A. There is one enzyme molecule in the asymmetric unit. A complete native data set has been collected from a rotating-anode source to a resolution of 2.7 A at 103 K, with an Rmerge of 6.7%.