Age-adjusted morbidity rates of Dengue Haemorrhagic Fever in Thailand during the period 1983-1987 were analysed. The 1983 data were used as standard baseline rates. The age-adjusted rates showed increasing trend in the disease morbidity, i.e., 60.2, 138.2, 159.6, 55.2 and 344.7 (per 100,000 capita) respectively. These rates were consistently higher than the crude rates. The Standardised Morbidity Ratios (SMRs) as compared with the baseline 1983 were 1.00, 2.30, 2.65, 0.92 and 5.73 respectively. Regional comparisons revealed annual increases in Bangkok areas, other Central provinces, the North and the Northeast with fluctuations observed in the South. The epidemic was most of the time higher in the Central provinces other than Bangkok areas. The authors suggest that age-adjusted rates (or possibly sex) should be applied in the study of DHF morbidity data, since there were discrepancies in the age distribution among different regions of the country.