It was recently reported that disease severity increased during the 1997 Cuban dengue 2 virus epidemic and it was suggested that this might be explained by the appearance of neutralization resistant escape mutants. We investigated these observations and ideas by sequencing 20 dengue 2 virus isolates obtained during the early (low case fatality rate) and the late (high case fatality rate) phases of the outbreak. Our results showed total conservation of the E gene sequence for these isolates suggesting that the selection of envelope gene escape mutants was not the determinant of increased disease severity. Alignment of these sequences with those available in GenBank, followed by Maximum likelihood phylogenetic analysis generated a tree, which indicated that our isolates are closely related to the virus that circulated in Venezuela in 1997/98 and subsequently in Martinique in 1998. This "American/Asian" genotype has therefore gradually dispersed across the Caribbean region during the past 5 years.