The most medically significant arboviruses causing human illness in south-east Asia belong to the genera Flavivirus (dengue, Japanese encephalitis, Kunjin, Zika, etc.) and Alphavirus (Chikungunya, Sindbis, Getah, etc.). All of these arboviral diseases are transmitted by mosquitoes. Dengue virus is the most prevalent arbovirus in south-east Asia and constitutes a major public health problem. Japanese encephalitis virus is also widespread in the region and symptomatic infection is associated with high mortality and severe neurological morbidity. Chikungunya virus causes mild but extremely painful illness. The number of Chikungunya cases has been increasing since early 2009. Epidemiological data show a steady, sometimes exponential, increase in the number of arbovirus infections in Asia. The spread of these viral infections can be linked to a number of complex factors.