Selection of priority areas in conservation biology should incorporate an evaluation of the contribution of imperilled species to the total species richness. To rank areas according to their conservation value, a new index – termed biodiversity conservation concern (BCC) – is proposed. This index combines the conservation status of each species belonging to a given species assemblage with the total species richness. In the BCC index, species are classified into categories of endangerment and weighted by the respective risk of extinction. The new method is applied here to the butterflies of the Aegean Islands (Greece) using different (national and international) red lists. Results were consistent with both classifications based on multivariate analyses and findings from other researches. The BCC index has two important features: it assigns a biodiversity value to an area based on many species, and it facilitates multi-species assessments of ecological effects.