BACKGROUND : Leak at the gastrojejunostomy (GJ) after Roux-en-Y gastric bypass is a rare but life-threatening complication. OBJECTIVE : To assess incidence, risk factors, treatment, and outcome of leaks at the GJ after Roux-en-Y gastric bypass in a nationwide cohort. METHODS : Sweden. METHODS : Leaks at GJ within 30 days postoperatively in 40,844 patients (age 41 yr, females 76%, and body mass index of 42.4 kg/m2) between 2007 and 2014 in the Scandinavian Obesity Surgery Registry were assessed. Register data and outcomes were verified by reviewing patient charts. Logistic regression was done to estimate odds ratios (ORs) for significant risk factors. RESULTS : Leak at the GJ was registered in 262 (.6%) patients, with 44% diagnosed within the first 3 postoperative days. Risk factors were male sex (OR 1.5 [1.1-1.9]), age ≥49 years (OR 1.9 [1.3-2.7]), diabetes (OR 1.4 [1.1-1.9]), conversion to open surgery (OR 3.9 [2.2-6.9]), and operative time ≥90 minutes (OR 2.6 [1.8-3.8]). In most patients, the leak resulted in a severe complication. Reoperative surgery was done in 85%, with the placement of a feeding gastrostomy in 24%. Stents were used at some time point in 31% of leaks. Of all patients with leaks, 25% required intensive care, 4% developed multiorgan failure, and 1% died. Median duration of stay for patients with leaks was 22 days, versus 2 days for others (P < .001). CONCLUSIONS : GJ leaks occurred in .6% of patients. Risk factors were male sex, age ≥49 years, diabetes, operative time ≥90 minutes, and conversion to open surgery. Surgical reintervention was common. Mortality was 1%.