An understanding of potassium dihydrogen phosphate, KH2PO4 crystal growth at the atomic scale first requires a correlation of the absolute structure and morphology with the chirality of its growth hillocks. This correlation is established here in four ways: by X-ray diffraction, by dyeing the growing surfaces with chiral molecules, as well as by determination of the signs of optical rotation, and the piezoelectric effect. We show that the (10 0) face, according to the X-ray coordinates given herein, is that face whose step edges run along the diagonal from lower right to upper left. (C) 2002 Elsevier Science B.V. All rights reserved.