Background: The Obesity Surgery Mortality Risk Score (OS-MRS) is a validated instrument for mortality risk prediction in patients undergoing laparoscopic Roux-en-Y gastric bypass (LRYGB) procedures classifying patients into low risk (class A), intermediate risk (class B), and high risk (class C). Objectives: The primary aim of this study was to evaluate the accuracy of the OS-MRS in predicting postoperative complications after LRYGB. Secondarily, the postoperative complication rate between primary and revisional LRYGB was systematically analyzed. Setting: The Obesity Center Amsterdam, located in a large teaching hospital, in Amsterdam, The Netherlands. Methods: The OS-MRS was applied to a consecutive database of patients who underwent LRYGB from November 2007 onwards. Postoperative complications were scored according to the Clavien-Dindo classification. Revisional LRYGB was separately analyzed. Results: LRYGB was performed in 1667 patients either as a primary (81.5%) or revisional (18.5%) procedure. The majority (n = 1371, 82.2%) were female, mean age 44.6 (standard deviation 14.4) years and mean body mass index 44.2 (6.5) kg/m(2). Nine hundred and four (54.2%) were OS-MRS class A, 642 class B (38.5%), and 121 (7.3%) class C. Complications occurred in 143 (10.5%) and 44 (14.2%) patients after primary and revisional surgery, respectively. In both primary and revisional LRYGB, there was no association between complications and the OS-MRS classification. Subanalysis comparing primary with revisional LRYGB found a significant association between revisional surgery and the development of severe complications (Clavien-Dindo >= 3) (P = .003) and mortality (P = .017). Conclusion: The OS-MRS was not an accurate predictor for postoperative complications in patients who underwent primary or revisional LRYGB. As in other studies, revisional surgery is an independent risk factor for the development of severe complications. (C) 2016 American Society for Metabolic and Bariatric Surgery. All rights reserved.