The objective of this study was to identify determinants of significant weight loss one year after gastric bypass surgery among United States veterans. Using data from the Veterans Affairs (VA) Surgical Quality Improvement Program, we identified 516 veterans who had gastric bypass surgery (24% laparoscopic) in one of twelve VA bariatric centers in 2000–2006 and one or more postoperative weight measures. The probability of losing 30% or more of baseline weight at one year was estimated via logistic regression, examining the following potential predictor variables: age, gender, race, marital status, body mass index (BMI), American Society of Anesthesiologists class, comorbidity burden, smoking status, diabetes medications taken and surgical procedure (open or laparoscopic). The 516 cases had a mean BMI of 49kg/m², mean age of 51.5 years, 74% were male, 77% were Caucasian, and 55% were married. The predicted mean weight loss was 76 (95% CI: 73–79) pounds (22%) at six months and 109 (95% CI: 104–114) pounds (32%) at one-year. Based upon estimated individual trajectories of 370 patients with adequate follow-up data, 58% of the sample lost 30% or more of their baseline weight at one year; and <1% lost <10% of their baseline weight at 1 year. In the logistic regression, patients were more likely to lose 30% or more of their baseline weight if they were female (odds ratio (OR)=2.5, p<0.01) or Caucasian (OR=2.3, p<0.01). We conclude that gastric bypass surgery yields significant weight loss for most patients in Veterans Affairs Medical Centers, but is particularly effective for female and Caucasian patients.