The Caribbean region has experienced a major surge in dengue activity in recent decades. Yet, for many, and especially the smaller islands, the true extent and general epidemiology of dengue transmission remains unclear because of inadequate systems of surveillance and reporting. We established an active surveillance system supported by laboratory-based diagnosis on the small island of Grenada, from January 2001 through June 2002. The surveillance data provided evidence of three distinct modes of disease dynamics in the form of low endemic, pre-epidemic, and overt epidemic transmission of mostly benign dengue fever. A shift in serotype activity and modal age was evident during the noted transition, with the more densely populated south end of the island presenting the focus of transmission.