Sixty-two Armillaria luteobubalina Watling & Kiledisease centres were assessed along the coast from near Cervantes, 160 kmnorth-west of Perth, to Cape Arid, 120 km east of Esperance. Disease centresranged from 0.02 to 6.5 ha in size (mean ± s.e., 1.7 ± 0.2 ha).Most disease centres were active, with mainly old deaths occurring in only7% of centres. Impact was low in only 3% of centres. Diseasecentres mainly occurred on calcareous sands of Holocene dune systems.Susceptible hosts from the Proteaceae, Mimosaceae and Myrtaceae tended to bedominant small trees or shrubs and their death resulted in centres composedmainly of sedges or small shrubs and ground-cover species from a range offamilies. Percentage cover of susceptible plant species was significantly lessin disease centres than adjacent healthy areas. Cover of resistant speciestended to be greater in disease centres than adjacent healthy areas, althoughdifferences were not significant. In association with changes in communitystructure, infection resulted in more bare ground in disease centres thanamongst healthy vegetation. Infection had minimal effect on species richness.The mortality progress curve for the susceptible species Dryandra sessilis (Knight) Domin increased at a meanapparent infection rate of 0.31 ± s.e. 0.12year-1. A disease centre extended at the rate of 0.004ha year-1 between 1964 and 1983 and 0.07 hayear-1 during the period 1981–1989. Diseaseextension per year was not correlated with yearly rainfall. Threatened taxakilled by A. luteobubalina included the rare andendangered Banksia brownii Baxter ex R.Br., B. occidentalis R.Br. subsp. formosa Hopper, and B. verticillata R.Br. This is the first report ofdisease significantly altering the structure and composition of coastalvegetation of south-western Australia. Armillaria luteobubalina is a significant additional,and hitherto unrecognised, selection pressure on coastal dune vegetationcommunities, and an important consideration in their management andconservation.