0 Chungue, E. Deparis, X. Murgue, B. 1998 Pacific Health Dialog 5 154-162 1998 Emergence of dengue epidemics worlwide has paralleled the expansion of the mosquito vector Aedes aegypti, together with jet air travel and increased urbanization. All four dengue virus serotypes (DEN-1, -2, -3, -4) have occurred in epidemic form during the last 50 years in French Polynesia. The first epidemic with known serotype was due to DEN-1 in 1944, during World War II. The disease disappeared from the Eastern Pacific after a Pacific-wide pandemic, but a series of epidemics at short intervals during two decades : DEN-3 in 1964-1965, DEN-2 in 1971, DEN-1 in 1975-1976, and DEN-4 in 1979. From 1980 to 1988, transmission of DEN-4 continued at a very low level until the resurgence of DEN-1 and DEN-3 in back-to-back epidemics in 1989. In 1996, DEN-2 reappeared in Tahiti and spread further into New Caledonia, the Cook Islands, Tonga, Samoa, and Fiji. As in most Pacific countries, epidemics with only one serotype have occurred in French Polynesia. Each time, genetic analysis of the causative viruses showed that the current epidemic was due to the introduction of a genotype different from the viruses recovered from past epidemics. These observations emphasize the need of an active clinical and virological surveillance for prevention and control of epidemics, together with molecular characterization of the viruses as part of the investigation of a dengue epidemic. As of now, a new genotype of DEN-2 different from that involved in the 1970s is disseminating throughout the Pacific region.