Data from 6246 participants aged 20-64 years (2339 males and 3907 females) in the cross-sectional phase of Tehran Lipid and Glucose Study (February 1999-May 2000) were used to determine distribution of serum lipid levels after 12-14 hour overnight fast. Mean total cholesterol (TC) concentration was 210 mg/dl. TC was significantly greater in females than males, 213 and 206 mg/dl, respectively (p < 0.0001). Thirty-one percent of population had TC values between 200 and 239 and 24% had values of 240 mg/dl or greater. Mean low-density lipoprotein cholesterol (LDL-C) was 129 and 135 mg/dl in males and females, respectively (p < 0.0001). Twenty-seven percent had LDL-C values between 130 and 159 and 23% had values 160 mg/dl or greater. The mean triglycerides (TGs) values were 190 and 162 mg/dl for males and females, respectively (p < 0.0001). The mean high-density lipoprotein cholesterol (HDL-C) was 39 in males and 45 mg/dl in females (p < 0.0001). The results showed higher levels of TC, LDL-C and TGs and slightly lower HDL-C in Tehranian adults than other studies in the industrialized countries.