We examined the assemblage of bats in a fragmented landscape along the northern coast of the island of Puerto Rico, West Indies, by mist netting and acoustic monitoring over a period of 25 months. Twelve of the 13 species present in the region were detected. It took nine nights of net and acoustic monitoring to detect 69% of the species, and 44 nights to reach 92%. Diversity was high, considering the insular nature of the assemblage and the fragmented nature of the ecosystem. We did not detect any important seasonal pattern in bat activity. The fruit eating bats at this study site are important importers of various seeds. Artibeus jamaicensis was most frequently captured and it appears to breed throughout the year at this location. Our results have important implications for management and conservation of biological diversity on tropical islands, and set a baseline against which the effect of further urban encroachment can be compared.