Trends towards increasing obesity in children threaten to undo achievements in the reduction of cardiovascular morbidity and mortality in adults. We sought to determine associations between physical activity, obesity and fasting lipid profile parameters in 147 hyperlipidemic children (50% males) being seen in 2 specialized lipid disorders clinics between 2/97 and 11/97. Mean age was 12.5±3.2 years. A self-administered questionnaire was developed to assess attitudes and time spent in various activities. Adiposity was determined as Z scores of age and sex standardized body mass index (zBMI). Mean (±SD) lipid parameters (mmol/L) were cholesterol 6.17±1.39, LDL 4.43±1.44, HDL 1.08±0.30 and triglycerides (TG) 1.51±0.89. Our patients were significantly more obese than normal, with a mean zBMI of +0.90±1.30 SD's (p<.0001 vs. population mean of 0); 21% >2 SD's above normal. Mean hours per week spent in physical activities was 14.2±14.0, with 22.9±13.0 hours spent in sedentary activities, including 15.5±9.1 hours watching TV. Relative to their peers, 30% of patients felt they were less active, and these patients spent significantly less time per week being active and more time being sedentary, and were younger and more obese than patients who felt their activity was similar or greater than their peers. Girls spent significantly less time playing video and computer games and were less obese than boys. Higher zBMI was significantly correlated with higher TG (r=0.33; p<.0001) but not with cholesterol or HDL, and was also correlated with greater time spent in sedentary activity (r=24; p<.004) and watching TV(r=26; p<.003). Increased time that other family members spent in phyical activity was significantly correlated with lower patient zBMI (rd.27; p<.002) and greater physical activity time of the patient (r=21; p<.02). Higher TG levels were significantly correlated with greater time spent in sedentary activity (r=26; p<.002) and watching TV (r=26; p<.002). Activity variables did not correlate significantly with cholesterol, LDL or HDL levels. Conclusion: Overall, this population was more obese than normal, and this adversely affected lipid profile parameters. Interventions aimed at increasing physical activity should be a part of the management of hyperlipidemic children, and should be directed to both the patient and their family.