To determine the effect of age and sex on cardiovascular risk factor expression in overweight children, data from clinical records of 497 overweight children (2-18 years of age) were examined. Data included average blood pressure (BP), fasting lipids, glucose, and insulin. The sample was stratified by age (younger than 11 and 11 years and older) and analyzed by sex. Subjects with an average BP > or = 90th percentile were classified as having high BP. Insulin and glucose were used in equations to estimate insulin sensitivity. Among subjects 11 years and older (n = 268), 52.6% of males had high BP compared with 32.6% of females (P < .001). Mean high-density lipoprotein cholesterol was lowest in the males 11 years and older compared with the females and younger males (P < .01). Triglyceride levels trended higher in males independent of age. In multivariate analyses, high BP was most strongly associated with age and severity of overweight while triglyceride level was most associated with sex and insulin resistance. The prevalence of high BP and dyslipidemia in overweight children is high. Overweight males 11 years and older have a higher prevalence of high BP and low high-density lipoprotein cholesterol than females and younger males. Greater cardiovascular risk factor expression in overweight males 11 years and older may explain the earlier appearance of cardiovascular disease end points in overweight men.