Aims: Recent estimates show the prevalence of obesity to be increasing at alarming rates. This study was conducted to examine trends of prevalence in overweight, obesity and central fat accumulation among Tehranian adults between 1998 and 2002. Methods: Height and weight of 2,102 adults, aged 20–80 years, participants of the Tehran Lipid and Glucose Study, were measured in 1998–1999 and remeasured in 2001–2002, after 3 years. Criteria used to state prevalence of overweight and obesity were body mass index (BMI) 25–29.9 and ≧30, respectively. Central fat accumulation was defined as waist-hip ratio (WHR) ≧0.8 in women and ≧0.9 in men. Individuals were divided into 10-year groups and the prevalence of obesity was compared according to sex and age. Results: In 1998–1999 and 2001–2002, mean BMI was 26.1 ± 4.1 and 26.7 ± 4.1 kg/m2 in men (p < 0.001) and 27.8 ± 4.9 and 28.7 ± 5.9 kg/m2 in women (p < 0.001), respectively. Mean WHR in women was 0.84 ± 0.08 in 1998–1999 and 0.88 ± 0.08 in 2001–2002 (p < 0.001). The prevalence of overweight in men was 42.5 and 46% and 40 and 39.5% in women in the two mentioned periods. The prevalence of obesity was 32.7 and 40.3% in men and 16.5 and 20.8% in women in 1998–1999 and 2001–2002 respectively. In both sexes the fastest increasing trends in obesity and central fat accumulation were seen in the 30- to 40- and 20- to 30-year-old age groups. Comparison of the 50th percentile of BMI in all age groups showed a significant increase in 2001–2002 as compared to 1998–1999 (p < 0.01). Conclusion: The findings demonstrate significant rises in the prevalence of both total and central fat accumulation, calling for urgent action to educate people in lifestyle modifications.