Sera obtained principally from children on the Caribbean islands of Aruba and Curaçao were tested for antibodies to various arboviruses. The test indicated that dengue 2 was endemic on Curaçao but not on Aruba, perhaps because of more effective vector control measures on Aruba. Neutralization tests performed with a samll number of sera suggest that dengue infections may have afforded some level of protection against yellow fever to a portion of the Curacao population.