The putative thiamine-biosynthesis protein PH1313 from Pyrococcus horikoshii OT3 has been overexpressed and purified. Crystallization was performed by the oil-microbatch method using 28%(v/v) 2-methyl-2,4-pentanediol as a precipitant at 291 K. A native X-ray diffraction data set at 1.9 A resolution and a single anomalous dispersion data set from a selenomethionine-derivative crystal at 2.1 A resolution were collected using synchrotron radiation at 100 K. The native crystal belongs to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 71.7, b = 71.2, c = 141.8 A.