Dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) are reportable diseases, the third most common causes for hospitalization of children in Thailand. Data collected from the Ministry of Public Health were analysed for trends. Rates of DHF increased in Thailand until 1987 when the largest epidemic ever, 325/100000 population, was recorded. Whereas the disease used to be confined to large cities, the rate is now higher in rural (102.2 per 100000) than urban areas (95.4 per 100000 in 1997). The age of highest incidence has increased, and the age group most severely affected is now those 5-9 years old (679/100000 in 1997). The case fatality rate has decreased with improved treatment and is now only 0.28%.