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Recent studies have demonstrated that mineral and electrolyte abnormalities develop in patients who undergo bariatric surgery. While it is known that these abnormalities are a risk factor for urolithiasis, the prevalence of stone disease after bariatric surgery is unknown. We evaluated the likelihood of being diagnosed with or treated for an upper urinary tract calculus following Roux-en-Y gastric bypass surgery.We identified 4,639 patients who underwent Roux-en-Y gastric bypass surgery and a control group of 4,639 obese patients who did not have surgery in a national private insurance claims database in a 5-year period (2002 to 2006). All patients had at least 3 years of continuous claims data. Our 2 primary outcomes were the diagnosis and the surgical treatment of a urinary calculus.After Roux-en-Y gastric bypass surgery 7.65% (355 of 4,639) of patients were diagnosed with urolithiasis compared to 4.63% (215 of 4,639) of obese patients in the control group (p <0.0001). Subjects in the treatment cohort more commonly underwent shock wave lithotripsy (81 [1.75%] vs 19 [0.41%], p <0.0001) and ureteroscopy (98 [2.11%] vs 27 [0.58%], p <0.0001). Logistic regression demonstrated that Roux-en-Y gastric bypass surgery was a significant predictor of being diagnosed with a urinary calculus (OR 1.71, CI 1.44-2.04) as well as undergoing a surgical procedure (OR 3.65, CI 2.60-5.14).Roux-en-Y gastric bypass surgery is associated with an increased risk of kidney stone disease and kidney stone surgery in the postoperative period. Clinicians should be aware of this hazard and inform patients of this potential complication. Future studies are needed to evaluate preventive measures in the high risk population.