Research shows that loss of control (LOC) eating impacts weight outcomes following bariatric surgery, but mechanisms explaining the development and/or maintenance of post-surgical LOC eating remain unclear. Ecological momentary assessment (EMA) research among eating disorder populations has demonstrated prospective relationships between negative affect (NA) and LOC eating; however, this momentary effect has not been examined among bariatric surgery patients. Thus, this study used EMA data to examine momentary relationships between NA and LOC eating among pre- and post-bariatric surgery patients.