Aims: To examine changes in anthropometric parameters and lipid profiles over a period of 3.6 years in an Iranian adult population according to body mass index (BMI) groups. Methods: Between 1998 and 2001 (phase 1) and 2002 and 2005 (phase 2), 5,618 nondiabetic Iranian adults aged >/=20 years were examined. Analysis of covariance was used to delineate trends in anthropometric parameters as well as total and low- and high-density lipoprotein cholesterol (TC, LDL-C and HDL-C, respectively) across BMI groups. Results: Although BMI increased in women, this increase was not significant in obese persons. Among the men, however, a significant increase in BMI was observed only in lean persons. Waist circumference (WC) increased across all BMI groups in both sexes. A significant decrease was observed in TC [men: -0.83 mmol/l, 95% confidence interval (CI) -1.27 to -0.40; women: -0.78 mmol/l, CI -0.97 to -0.60] and LDL-C (men: -0.63 mmol/l, CI -1.13 to -0.13; women: -0.51 mmol/l, CI -0.78 to -0.24). A significant decrease in mean HDL-C was observed only among men (-0.09 mmol/l, CI -0.13 to -0.04), with no difference among BMI groups (p = 0.3). There were no significant decreases in TC/HDL-C and LDL-C/HDL-C ratios in men or women. Conclusions: Despite an increase in WC, favorable trends were observed in TC and LDL-C levels. The favorable trend in TC levels was counterbalanced by changes in HDL-C, as reflected by the absence of a significant decrease in TC/HDL-C or LDL-C/HDL-C. Copyright © 2008 S. Karger AG, Basel