The small size, degree of isolation, and particular evolutionary processes occurring in islands makethem highly diverse and an essential target for conservation. For the same characteristics, they are alsoextremely vulnerable to human-mediated disturbances. During the last centuries, nearly 80% of speciesextinctions have occurred on islands. While there is information on the human threats, level of protection, and conservation importance of islands, an integrative picture combining these aspects and aimed atdetermining conservation priorities to inform decision-making is still missing. Here, we jointly analyzedthese three aspects producing a worldwide island conservation assessment based on terrestrial vertebrates. Considering the Aichi target of >17% of protection and all protected area categories, we found that5397 islands, encompassing a quarter of the worldwide island area, face high human modification andhave a low level of protection, with 33% of them showing extreme levels of human modification. Also, if we were to consider the new threshold of protected area coverage proposed to accurately protect theworld’s biodiversity and ecosystems (Nature Needs Half initiative), 77% of the world’s islands would facethis dramatic scenario. Furthermore, most large islands harboring the highest number of threatened vertebrates are found on this critical situation (low protection and high human modification). Based on theanalysis of these conservation scenarios, we identified potential priority islands that provide opportunities to improve island conservation worldwide. The mbest opportunities are located in 58 islands witha low level of protection and human modification, which harbor more than 5 threatened vertebrates’species and are located in different regions of the world. (c) 2022 Associac,similar to ao Brasileira de Ci <^{}>encia Ecol ` ogica e Conservac, similar to ao. Published by Elsevier B.V. This is anopen access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).