Antibodies to group B arbovirus were common among coastal populations in the Haitian part of the Caribbean island of Hispaniola. Antibodies were present in 43% of children one to five years old; prevalence in older persons increased with age. In nine asymptomatic persons serodiagnostic changes indicative of group B arbovirus were detected during six of twelve consecutive months. In port cities where antibodies were common in children, Aedes aegypti indices of 50%-70% were observed; in contrast, no A. aegypti mosquitoes were found in an inland village in which children lacked denjue hemagglutination-inhibiting antibodes. Between 1969 and 1971, dengue 2 virus was isolated from 11 persons with episodic febrile illnesses, although no epidemic was apparent. These findings indicate that dengue virus infection was endemic in Haiti during the period of the study.