To determine the body mass index (BMI) located at the fulcrum of success and failure in a prospective study conducted at the University of Texas Health Science Center at Houston. On average, our patients whose percentage of excess weight loss (%EWL) was >50% at 1 year had a significantly lower BMI than those with <30% EWL.We prospectively collected the weight loss data for 430 patients who had had an adjustable gastric band placed. We stratified the %EWL within 1 year for patients with a BMI of 30–59 kg/m 2 . A line was generated for the %EWL over time for BMI groups of 30–39, 40–49, and 50–59 kg/m 2 and compared with the average %EWL over time. The y-intercepts of the resulting four lines were graphed against the average BMI for each group.The generated y-intercept line had an R 2 of .9237. Using the equation of this line and the known y-intercept for the average, we solved for x, resulting in a BMI of 46 kg/m 2 . Patients with a BMI <46 kg/m 2 had a 50% EWL at 1 year, and those with a BMI >46 kg/m 2 had only a 33% EWL at 1 year. The %EWL between the groups was significantly different at all measured intervals (P <.0001).A BMI of 46 kg/m 2 identifies those at high risk of failure to lose a significant percentage of excess weight after adjustable gastric banding and who require closer follow-up. Furthermore, patients who have a BMI >46 kg/m 2 should be advised that their weight loss might be suboptimal at 1 year.