A new introduced species of psyllid, Ctenarytaina peregrina sp. n., is described from the UK and Eire, where it is causing economic damage to commercially grown Eucalyptus parvula, a species otherwise known as small-leaved eucalyptus, Eucalyptus parvifolia or kybean gum. The separation of C. peregrina from the other introduced European species of economically important Eucalyptus-feeding Ctenarytaina, C. eucalypti and C. spatulata, is discussed and a key for their identification is provided. C. peregrina remains unknown in Australia but its host plant, E. parvula, is native to eight restricted localities at upland sites in New South Wales, where it is considered a rare and endangered species.