In contrast to the extraordinary adaptive radiation of Caribbean Anolis lizards, head-first burrowing worm lizards (Amphisbaenia) of the Greater Antilles show a high degree of evolutionary conservatism in both taxonomic and phenotypic diversity. While Caribbean anoles reach over 160 endemic species and six ecomorphs, amphisbaenians peak at one to seven species per island and are characterized by two distinct head shapes, each associated with a specific burrowing behaviour. Using three-dimensional landmark-based geometric morphometrics, we found that Caribbean amphisbaenians also occupy a relatively confined area of skull morphospace, with considerable overlap between species from different islands and strong morphological integration between crania and mandibles. The only exceptions were the bizarre keel-headed cadeids (Cadea) from Cuba, which appear to be unlike other round-headed Caribbean forms and closer to Mediterranean blanids (Blanus), their putative sister group. The only significant differences in skull shape were found between insular amphisbaenians and their mainland relatives, indicating that fossorial vertebrates may respond differently to ecological opportunity than other terrestrial fauna. Given their highly specialized subterranean niche, we suggest that worm lizards are under strong stabilizing selection to maintain cranial proportions for head-first digging, thus limiting their ability to exploit novel resources (e.g. microhabitat, prey) encountered in insular environments.