Background: Obesity is a rapidly progressing pandemic and a central feature of the metabolic syndrome. There is no solid evidence on the recent trends of obesity in Iran. In this study we present the secular trends of overweight and obesity among Iranian adults (25-64 years old) within an 8-year period (1999-2007). Methods: The analyses were performed on the datasets of three cross-sectional national surveys: The National Health Survey-1999 (n = 21,576), National Surveys of Risk Factors for Non-Communicable Diseases (SuRFNCD)-2005 (n = 70,945), and SuRFNCD-2007 (n = 4,186). Results: The overall prevalence of obesity increased from 13.6% in 1999 to 19.6% in 2005 and 22.3% in 2007 [odds ratio (OR) = 1.08 per year; P < 0.001]. For overweight subjects, the rates were, respectively, 32.2%, 35.8% and 36.3% (OR = 1.02 per year; P < 0.001). During these years, the mean body mass index (BMI) (kg/m2) increased from 25.03 in 1999, to 26.14 in 2005, and 26.47 and 2007 (P < 0.001). The increase in prevalence of obesity was seen in both males (OR = 1.09 per year; P < 0.001) and females (OR = 1.07 per year; P < 0.001) and both urban (OR = 1.07 per year; P < 0.001) and rural (OR = 1.10 per year; P < 0.001) residents. Conclusions: In conclusion, the present study highlighted the rapid growth of obesity during recent years in Iran. Our findings indicate the crucial necessity of primary prevention programs to counteract this undesired condition.