The objective of this retrospective cohort study was to evaluate the effectiveness of the Duke University Healthy Lifestyles Program (HLP), a primary care-based childhood obesity treatment program. The study population included obese 2- through 19-year-old patients who entered the HLP between October 2006 through December 2008 and who had a visit to the HLP between the sixth and eighth month after entry. Most of the 282 patients were female (57%) and non-Hispanic/non-White (61%). The median age was 11 years. At baseline, the mean body mass index standard deviation score (BMI SDS) was 2.51, and patients achieved a mean reduction in BMI SDS of 0.10 (standard deviation = 0.20). For patients with baseline and follow-up measures of comorbidities, there were improvements in blood pressure, triglycerides, total cholesterol, and insulin resistance (P < .05). The patients in our obesity program demonstrated a small reduction in the severity of obesity. Improvements occurred in some obesity-associated comorbidities.