Smoking and smoking cessation are presumed to have associations with body weight and central adiposity. This study aims to investigate the relationship between these factors in a large sample of the Iranian adult population. We collected the data regarding smoking status, weight, height and waist circumference (WC) from 5287 Iranian individuals aged 15-64 years who participated in the third national surveillance of risk factors of non-communicable diseases (SuRFNCD) in March 2007. The BMI and WC values were investigated in smoker, ex-smoker and never-smoker groups using univariate and multivariate analyses. In the univariate analysis, ex-smokers had significantly higher rate of general obesity (p=0.002), central obesity (P<0.001), mean BMI (p<0.001) and mean WC (p<0.001) compared to the current smoker group. Although smokers had significantly lower rate of obesity (p=0.003) and mean BMI (p<0.001) compared to non-smokers, they had significantly higher WC (p=0.016). Interestingly, among female subjects, smokers had higher rate of obesity (p=0.006) and BMI (p=0.006) than non-smokers, while ex-smokers were not more obese than smokers. However, smoking status was not independently associated with obesity or central obesity in the multivariate regression analysis. Since smoking seems to be associated with higher risk of central obesity, the misleading notion that smoking causes weight loss should be avoided. Iranian women should be more cautious if they tend to stay slim by the false belief that smoking induces weight loss.