BACKGROUND The purpose of this study was to determine whether age is a predictor of sensitivity to the peripheral effects of insulin on carbohydrate metabolism independent of the potential influences of the level of sympathetic nervous system (SNS) activity and blood pressure (BP). METHODS In 60 human subjects (age range 19-78 years), insulin sensitivity, SI, was determined from glucose and insulin levels obtained during an intravenous glucose tolerance test, and plasma norepinephrine (NE) levels were measured to estimate SNS activity. RESULTS There were age-associated increases in plasma NE level (r = .585; p < .001) and mean arterial BP (r = .516; p < .001), and an age-associated decline in SI (r = -.352; p = .04). However, in stepwise multiple regression analysis, body mass index (BMI) and mean arterial BP were the only independent predictors of SI, accounting for 43% of the variance in SI; age, plasma NE level, plasma epinephrine level, and fasting plasma glucose did not enter the model. Although these results suggest an age-associated decline in insulin sensitivity, this decline appears to be associated with BMI and mean arterial BP rather than aging per se. In addition, the age-associated increase in SNS activity was not found to be an independent predictor of insulin sensitivity. CONCLUSIONS This study demonstrates that in addition to BMI, blood pressure should be considered as another confounding factor in studies of insulin sensitivity in human aging.