Dengue, the most important human arboviral disease, is transmitted primarily by Aedes aegypti and, to a lesser extent, by Aedes albopictus. The current distributions of these invasive species overlap and are affected by interspecific larval competition in their container habitats. Here we report that competition also enhances dengue infection and dissemination rates in one of these two vector species. We determined the effects of competition on adult A. aegypti and A. albopictus, comparing their susceptibility to infection with a Southeast Asian strain of dengue-2 virus. High levels of intra- or interspecific competition among larvae enhanced the susceptibility of A. albopictus to dengue virus infection and potential for transmission, as indicated by disseminated infections. Doubling the number of competing larvae (A. albopictus or A. aegypti), led to a significant (more than 60%) increase in the proportion of A. albopictus with disseminated dengue-2 infection. Competition-enhanced vector competence appears to result from a reduction in 'barriers' (morphological or physiological) to virus infection and dissemination and may contribute to the importance of A. albopictus in dengue transmission. Similar results for other unrelated arboviruses suggest that larval competition, common in mosquitoes, should be considered in estimates of vector competence for pathogens that infect humans. © 2007 The Royal Society.