The crystal structure of synthetic Trippkeite, atheta=8.59, ctheta=5. 57 A; space group P4mbc-D13/4h, Z=4, has been refined from 270 independent reflections to R=0.059. The structure type determined for a natural sample was confirmed. The Cu-atoms are coordinated by a distorted tetragonal bipyramid of six oxygens. The As atoms are coordinated by three oxygens to form a trigonal pyramid. The Cu polyhedrons are connected by common edges, the As polyhedrons by common corners, making chains parallel to the fourfold axis.