To document the effect of anastomotic leaks on morbidity and mortality after Roux-en-Y gastric bypass (RYGB) for obesity. Design: Prospectively collected data on 840 consecutive patients who underwent RYGB between 1998 and 2005. Multivariate logistic regression analysis was used to determine the effect of anastomotic leaks on postoperative morbidity independent of sex, age, preoperative body mass index, access (open vs laparoscopic), calendar year of RYGB, and comorbidities. P Ͻ.05 was considered significant. Results: A total of 36 patients (4.3%) developed leaks after RYGB. Patients who developed anastomotic leaks had a significantly higher overall complication rate (61% vs 20%, PϽ.001), mortality (14% vs 4%, P=.01), and duration of hospital stay (24.5 vs 4.5 days, P Ͻ.001) compared with patients who did not develop leaks. In a mul