The aim of this study was to examine the effects of age, time period, and birth cohorts with dengue fever/dengue hemorrhagic fever (DF/DHF) in Bangkok, Thailand over the period 1981-2000. The age group at greatest risk for DF/DHF was 5-9 years old. The period effect shows a remittent pattern, with significant increases in 1986-1990 and 1996-2000. The birth cohort group showed a significant decreasing trend from the 1961-1965 group to the 1991-1995 group (R2 = 0.7620) with a decreasing rate of 0.1. We concluded that the temporal trend of DF/DHF is decreasing; especially for DHF.