The helminth fauna present in the gut contents of Iberian adders,Vipera seoanei(Squamata: Viperidae), were characterised and analysed in respect to biological and eco-geographic factors that may affect the occurrence and diversity of helminths in this species. A total of 317 samples of preserved stomachs and intestines, covering the distributional range ofV.seoanei, were examined. Similar to otherViperaspecies from the Iberian Peninsula, the helminth fauna was also impoverished inV.seoanei, but unlike otherViperaspecies from Central and East Europe, helminths were mostly found in adult vipers, and occurred in vipers located at the periphery of the species range, characterised by low elevation, high temperature and precipitation levels, and abundant pastures.