On West Indian islands, as elsewhere in the world, ants are a very important component of virtually every terrestrial ecosystem. Nonetheless, the ants of most West Indian islands have remained largely unknown and unstudied. Now several destructive exotic ant species are spreading through the region, threatening native biodiversity. Here, we have compiled published and unpublished ant records and collected new specimens to document the diversity of ants on the island of Grenada. Our investigations increased the list of ant taxa known from the island to 82 (65 New World and 17 Old World species). Of these, 71 species are represented among specimens we collected, whereas 11 are New World species known from Grenada solely on the basis of earlier records. Some species recorded earlier, including at least nine not seen for more than 100 years, may now be extinct on Grenada. Grenada has more New World ant species than are known for Barbados (46), a neighboring island that has 34% more land area. Factors that may contribute to this difference include: 1) during low sea levels 15,000 years ago, Grenada was part of a larger island about 10 times Grenada's current size; 2) Grenada is more mountainous than Barbados; and 3) Grenada has more remaining forest cover than Barbados (50.0% vs. 14.7%). Conversely, Grenada has fewer Old World ant species than are known for Barbados (24). Factors that may contribute to this difference include: 1) lower human population density, 2) lower levels of imported lumber products, and 3) lower tourism levels. Records for only four of the 17 Old World exotic ants found in Grenada date to before 1995. Major tramp ant species that are known from the West Indies but have not yet been recorded from Grenada include Old World species such as the pharaoh ant (Monomorium pharaonis), the African big-headed ant (Pheidole megacephala), and the difficult white-footed ant (Technomyrmex difficilis), as well as the red imported fire ant (Solenopsis invicta).