San Andrés, the largest island in the Colombian Caribbean, Archipelago of San Andrés, Providence and Santa Catalina, include characteristic tropical coastal ecosystems, which provide habitat for the semiterrestrial crab Cardisoma guanhumi. Between March and April 2012 a study was conducted aiming to make a preliminary evaluation of the crab population on the island. 101 adults crabs were collected manually and their main morphometric measurements were taken (carapace length and width and weight), as well as sex information. Males were more numerous (male: female sex ratio 3:1) and grew larger in terms of body weight and carapace. The species does not have any signifiant predators on the island and they are not considered by the islanders an economically important resource in this area; this may allow crabs to reach larger sizes compared to other localities along their geographical distribution. This is why the island of San Andres should be considered as a natural refuge for the species, since in other Colombian regions it is considered a vulnerable species.