The genetic structure of marram grass populations at coastal and inland locations,200 m apart, was investigated at three sites by means of amplified fragmentlength polymorphism (AFLP) DNA markers. We expected a genetic differentiation betweencoastal and inland populations and more genetic variation in the coastal areas as a resultof different events of colonization by different plant materials. An assignment testshowed that the sampled Ammophila arenaria could be assigned to twogroups based on AFLP data. The spatial distribution of the two AFLP types of A.arenaria varied with sampling location. In two of the three locations, mainlyone type (1) was found in the newly formed dunes. This type did also occur furtherlandward, but the second type (2) was preferentially found in inland populations. Geneticdiversity was very low and of similar value in both coastal and inland populations. Foreach site, outlier loci with respect to FST value wereidentified, which may be indicative of different selection pressures in coastal comparedwith inland clusters. However, no identical outlier loci were found at all three sites.Possible explanations for the observed difference in distribution of type 1 and 2populations between coastal and inland sites are discussed.