The aim of this study was to evaluate an intensive lifestyle intervention for weight management among youth in a primary care setting on insulin sensibility, compared to a control group. The study included 42 youths 9-17 years old (n=23 intensive lifestyle intervention, n=19 control group) who completed a randomized trial for weight management in a primary care setting which included an oral glucose tolerance test. The intensive lifestyle intervention included monthly consultations with the primary care physician, nutrition counseling with a registered dietitian (weekly first 3 months and then monthly) and 12 group sessions in a behavioral change protocol. The control group attended monthly consultations with the primary care physician. Insulin sensitivity was estimated by the Insulin Sensitivity Index ISI(0,120) at baseline and 6 months posttreatment. At 6 months, the mean +/- DE, increase in insulin sensitivity was greater in the intensive lifestyle intervention than the control group (+46.8 +/- 56 vs. +5.6 +/- 47, between-group difference 41.2 [CI 95%, 8.5, 73.9], p = 0.01): Sixty five percent of youths on the intensive lifestyle intervention increased insulin sensitivity over 9 units vs. 32% in the control group (p=0.03). This study shows preliminary evidence that an intensive lifestyle intervention program can be an alternative model to improve insulin sensitivity among youths in the primary care setting.