We revise the taxonomy of the two parakeet taxa in the psittaciform genus Eunymphicus – E. cornutus cornutus (Horned Parakeet) and E. c. uvaeensis (Ouvéa Parakeet) – which are restricted to New Caledonia and the Loyalty Islands, in the south-western Pacific, and we investigate their relationship with the genera Cyanoramphus, considered traditionally as its closest related genus, and Prosopeia. We used three sets of characters to assess the level of differentiation between the Eunymphicus taxa: behaviour (vocalisations), morphology (biometrics and plumage coloration) and genetic (mitochondrial cytochrome b DNA sequence variation, 924 nucleotides). The analysis of vocalisations revealed significant differences, as did morphological analyses (size and number of feathers of the crest, size of the bill, and colour pattern of the head). Genetic distance between the Horned and Ouvéa Parakeets is similar to that recorded between closely related species of Cyanoramphus and both taxa possess novel and diagnostic synapomorphic substitutions. From these genetic, behavioural and morphological data, the two Eunymphicus taxa should be considered separate species, a suggestion that is supported by ecological data as well as anecdotal data on hybridisation from captive birds. Our molecular data also support the traditional view that Cyanoramphus is the closest relative of Eunymphicus, with Prosopeia a sister group to this clade. The consistency with which Platycercus clusters next to the Cyanoramphus–Eunymphicus–Prosopeia grouping suggests that Platycercus may well be the next closest relative of this clade.