Technical Abstract: Relationships have been detected between the metabolic risk factors of mothers and their children, but there is little information about whether these relationships were due to genetic/biological or environmental (e.g. physical activity) factors. To assess the relationship between the metabolic risk factors of 122 mothers and their 6-7 year old children and the Influence of physical activity and ethnicity on this relationship in a tri-ethnic (EA, AA & Hispanic) sample. Mother and child fasting insulin, HDL, LDL and triglycerides, waist circumference, systolic and diastolic blood pressure, height and weight, and BMI were recorded. Maternal physical activity was assessed using a seven-day recall. Child physical activity was assessed using heart rate monitoring, with the mean number of minutes above 140 bpm and 50% Maximal Heart Rate Reserve per day calculated from an average of 6.6 days of monitoring across 3 years. Correlational methods were used to describe the relationship between risk factors, demographics, and physical activity level among the mothers and children. Chi-square tests of independence were used to examine the relationships between race and other variables. There were significant positive associations between mothers and child's BMI, Waist circumference, HDL, LDL, systolic blood pressure and insulin levels (r = 0.20 to 0.37, p<0.05). Neither mother nor child physical activity levels were significantly associated with any of the other risk variables. The physical activity levels of mothers and children were not associated. Controlling for mothers or mother and child activity levels did not change any of the parent child metabolic risk factor relationships. There were significant (p<0.05) ethnicity differences in the relationship between mothers and child's waist circumference and insulin levels. In conclusion, physical activity, an environmental factor, did not modify the relationship between the metabolic risk factors of mothers and their children, but there were associations that differed by ethnicity. This pattern of results supports a more biological interpretation of significant mother-child relationships for metabolic syndrome risk factors. Research should examine the Influence of other possible environmental factors on these relationships.