Objective-The aim of this study was to examine the association of physical activity with glucose tolerance and resting energy expenditure (REE) among adolescents. Research design and methods-Subjects were 32 male and female adolescents aged 12-18 years. Intravenous glucose tolerance (Kg) and REE were assessed under inpa-tient conditions after an overnight fast. K g was determined as the inverse slope of time versus (ln) glucose over minutes 8-19 of an intravenous glucose tolerance test. Physical activity was assessed over 8 days using accelerometry (counts per minute). Results- In multiple linear regression analysis, Kg was positively associated with total physical activity (TPA), moderate physical activity (MPA), and 5-min bouts of MPA. Similarly, REE was positively associated with TPA, MPA, and 5-min bouts of MPA. Conclusions- In this population, physical activity was positively related to both glucose tolerance and REE. These results suggest that moderate activity may be beneficial in the prevention of diabetes in adolescent populations both through promoting efficient glucose disposal and through increasing energy expenditure. © 2009 by the American Diabetes Association.