Chorismate synthase (EC 4.6.1.4) catalyzes the transformation of 5-enolpyruvylshikimate 3-phosphate to chorismate in the last step of the shikimate pathway. Chorismate synthase from Helicobacter pylori fused with an eight-residue C-terminal tag was overexpressed in soluble form in Escherichia coli. It was crystallized at 296 K using polyethylene glycol 400 as a precipitant. A set of X-ray diffraction data was collected to 2.5 A resolution using synchrotron radiation. The crystals belong to the tetragonal space group I4, with unit-cell parameters a = b = 145.79, c = 130.98 A. The asymmetric unit contains a tetramer, giving a crystal Volume per protein mass (V(M)) of 2.13 A(3) Da(-1) and a solvent content of 42.3%.