The origins of obesity and metabolic syndrome occur early in childhood; therefore understanding the impact of physical activity and stress on obesity and related metabolic diseases is an important child health issue. PURPOSE: The purpose of this study was to examine the moderating effects physical activity may have on the relationship between measures of stress (via waking salivary cortisol and various self-report measures) and the components of the metabolic syndrome in 8-18 year old males. METHODS: Participants were 37 males ages 8 to 18 yrs. Anthropometrie variables were determined by standard procedures. Physical activity was assessed using the MTI Actigraph accelerometer. Television viewing (TV) and video game playing times were assessed via questionnaire. Waking salivary cortisol was assayed using a commercially available ELISA kit. Self-report measures of stress were assessed using the Physical Appearance Related Teasing Scale, Perceived Stress Scale, Children's Depression Inventory, State-Trait Anxiety Inventory for Children, and Self-Esteem Questionnaire. Blood pressure was measured according to American Heart Association procedures. Blood cholesterol and HbA1c were collected by finger prick and assessed using a desktop analyzer. A composite score for the metabolic syndrome was generated by summing the age-standardized z-score for HbA1c, MAP, HDL-C, and WC. RESULTS: Approximately 27% and 16% of the sample were overweight or obese, respectively. Correlations between physical activity and metabolic syndrome were low, but in the expected direction after adjustment for age and maturity offset (r<-0.13). TV and video games playing time was significantly associated with the metabolic syndrome score (r= 0.39 and 0.43, respectively). Correlations between stress-related variables and the metabolic syndrome score yielded significant associations between school-related self-esteem (r=-0.46) and general appearance related teasing (r=-0.36). Associations between stress-related variables and the metabolic syndrome score in high and low physical activity groups showed significant associations between school- and sports-related self-esteem (r=-0.64 and -0.53, respectively) and trait-anxiety (r=0.53). CONCLUSION: The results suggest that a significant relationship exists between stress and the metabolic syndrome score. Additionally, the results suggest that physical activity may buffer the effects of stress on metabolic syndrome.