Bariatric surgery achieves long-term weight loss in obese adults with improvement of diabetes and hypertension. Little is known about the effect of this weight loss on renal parameters. We performed a retrospective study of 94 obese adults who had Roux-en-Y gastric bypass surgery with a mean 12-month follow-up. Baseline (preoperative) mean age was 49 years, 76% were female, 37 had blood pressure (BP) >or= 140/90 mmHg and 32 had Type 2 diabetes. 73 patients had normoalbuminuria (urine albumin creatinine ratio (ACR) <30 mg/g) while 21 had microalbuminuria (ACR 30<300 mg/g). At follow-up (postoperative), we observed a decrease in mean body weight (133.6 to 97.9 kg, p<0.0001), mean hemoglobin A1c (6.3 to 5.6%, p<0.0001) and mean systolic blood pressure (132.7 to 114.0 mmHg, p<0.0001). There was a significant reduction in ACR (median with interquartile range) from 9.5 (5-28) to 5.5 (3-10) mg/g, p < 0.0001. Fewer patients had microalbuminuria (22.2 to 6.2%, p=0.004) after surgery. Subgroup analysis revealed that significant decrease in ACR was present in the 32 patients with diabetes (16.5 (5-67) to 6.0 (4-11) mg/g, p=0.001) and in the 37 patients with metabolic syndrome (8.0 (5-16) to 6.0 (3-13) mg/g, p=0.012), while 25 patients with obesity alone had a lower ACR (6.5 (4-13) to 4.5 (3-8) mg/g, p=0.270). Multiple linear regression analysis showed change in hemoglobin A1c (p=0.011) and baseline level of ACR (p<0.0001) to be significantly associated with change in ACR. We conclude that obese adults have a reduction in albuminuria after surgical weight loss, most importantly in patients with diabetes or metabolic syndrome.