Kikuchi diffraction was used to accurately determine the orientation relationship (OR) between Mg17Al12 precipitates and matrix in an AZ91D alloy. For both continuous and discontinuous precipitations, the Burgers OR and the Potter OR were equally observed. The lattice parameter of Mg17Al12 associated with the former is bigger than that of the latter. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.