Data from 3148 participants aged 3-19 years (1447 males and 1701 females) in the cross-sectional phase of Tehran lipid and glucose study (February 1999-May 2000) were used to determine serum lipid levels [total cholesterol (TC), triglycerides (TGs), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C)] after 12-14 hours overnight fast. The values were analyzed by sex and age. Mean serum TC concentration was 170 mg/dl. TC was significantly greater in females than males (173 vs. 167 mg/dl, p < 0.05). The 90th and 95th percentiles for serum TC were 211 and 227 mg/dl, respectively. There was a significant decrease in mean TC in males during puberty. Thirty-one percent of population had TC values between 170 and 199 mg/dl and 16% had values of 200 mg/dl or greater. The mean TGs values were 103 for males and 108 mg/dl for females [non-significant (NS)]. The prevalence of high-risk values of TGs increased with age in males, reaching a peak at 17-19 years. The mean HDL-C level was 45 mg/dl. Mean HDL-C was highest at 7-10 years of age and decreased thereafter. The mean LDL-C was 102 in males and 107 mg/dl in females (NS). Twenty-two percent had LDL-C values between 110 and 129 mg/dl and 17% had values 130 mg/dl or greater. The results showed higher levels of TC, LDL-C and TGs and lower HDL-C in Tehranian children and adolescents than other studies. To design comprehensive public health programs to reduce serum lipid levels among Iranian children and adolescents, underlying factors for the high prevalence of dyslipoproteinemia should be sought.