Introduction and hypothesis: Prior studies demonstrate mixed results on the impact of obesity on the success of midurethral slings (MUS), with little known about how postoperative weight change affects outcomes. We aimed to examine the effect of postoperative weight change on outcomes 12 months after MUS for stress urinary incontinence (SUI). Methods: This secondary analysis utilized data from two multicenter randomized trials of women undergoing MUS placement. Subjects were categorized into cohorts based on change in body weight at 12 months postoperatively: weight gain (?5% increase); weight loss (?5% decrease), and weight stable (<5% change). The primary outcome was SUI cure (no SUI episodes in a 3-day bladder diary). Patients with mixed urinary incontinence (MUI) were analyzed for changes in daily average urge incontinence (UUI) episodes in a 3-day diary. Penalized logistic regression assessed the impact of demographic and perioperative variables on the primary outcome. Results: Of the 918 women included, 635 (70%) were weight stable, 144 (15%) had weight gain, and 139 (15%) had weight loss. Patients in the weight loss cohort had a higher smoking rate and a higher baseline body mass index (SD 0.29, 2.7 respectively). All cohorts experienced high SUI cure rates ranging from 77 to 81%, with no significant difference in SUI cure between cohorts (p = 0.607). Of 372 subjects with MUI, the weight loss cohort had significantly greater improvement in UUI episodes. Conclusions: Weight change at 12 months postoperatively did not significantly alter efficacy of MUS for treatment of SUI. Patients with MUI who lost ?5% body weight had significantly greater improvement in UUI episodes.