A root-lesion nematode, Pratylenchus dunensis sp. n., is described and illustrated from Ammophila arenaria (L.) Link, a grass occurring abundantly in coastal dunes of Atlantic Europe. The new species is characterised by medium sized (454-579 μ m) slender, vermiform, females and males having two lip annuli (sometimes three to four; incomplete incisures only visible with scanning electron microscopy), medium to robust stylet (ca 16 μ m) with robust stylet knobs slightly set off, long pharyngeal glands (ca 42 μ m), lateral field with four parallel, non-equidistant, lines, the middle ridge being narrower than the outer ones, lateral field with partial areolation and lines converging posterior to the phasmid which is located between the two inner lines of the lateral field in the posterior half of the tail, round spermatheca filled with round sperm, vulva at 78% of total body length and with protruding vulval lips, posterior uterine sac relatively short (ca 19 μ m), cylindrical tail (ca 33 μ m) narrowing in the posterior third with smooth tail tip and with conspicuous hyaline part (ca 2 μ m). Males occur abundantly and present similar characteristics except for smaller dimensions for all morphological characters, but the head region is more truncated in outline than the female, spicule length is ca 15 μ m and testis length is ca 195 μ m. Nucleotide sequences of the rDNA expansion region D2D3 differed from the morphologically similar species P. penetrans and P. brzeskii that also occur in coastal dunes. These differences are supported by PCR-RFLP of the ITS-rDNA. Pratylenchus dunensis sp. n. was also found parasitising roots of Elymus farctus Viv.