Aim: Our objective was to reconstruct a species-level phylogeny of the genus Delias, to elucidate their finer-scale biogeography and to test boundaries between closely related taxa. Location: Indo-Australian region, with a focus on Wallacea. Methods: Sequence data from 131 taxa, representing all recognized species groups and more than half of the known species of Delias, were used in the analysis. Phylogenetic analyses based on molecular characters of the mitochondrial gene cytochrome c oxidase subunit I (COI) and nuclear genes wingless and elongation factor 1α (EF-1α) were carried out using maximum parsimony and Bayesian inference. Biogeographical reconstructions were undertaken using the parsimony-based method dispersal-vicariance analysis and the dispersal-extinction-cladogenesis model as implemented in rasp and Lagrange, respectively. Results: The phylogenetic hypothesis resolved 14 distinct clades, here designated the nysa, isse, pasithoe, belladonna, ladas, geraldina, aroae, eichhorni, sagessa, aganippe, hyparete, belisama, albertisi and nigrina species groups. Delias blanca Felder and Delias chrysomelaena Snellen van Vollenhoven were transferred to the pasithoe and isse species groups, respectively. We demonstrate that the barcode region of COI is useful for the delineation of closely related, more recently diverged, Delias species. Species diversification in Delias, for the most part, is shown to pre-date the Pleistocene, even in montane mainland New Guinea where numerous phenotypically similar sister species co-occur. Main conclusions: Sibling Delias species found in sympatry are largely restricted to those clades confined to mainland New Guinea, where most species occur in high-elevation habitats. Conversely, clades with large geographical ranges are composed of essentially allopatric taxa. Although an Australian Plate origin is plausible for the genus, Delias is likely to have colonized islands peripheral to Australia during the early stages of its evolution (i.e. during the Miocene), as evidenced by the presence of older lineages in Wallacea and also in islands of the south-western Pacific. © 2012 Blackwell Publishing Ltd.