objective: to evaluate the oxidative stress and inflammatory markers in obese patients before and after roux-en-y vertical banded gastroplasty. methods: we studied 20 class iii obese patients undergoing roux-en-y vertical banded gastroplasty, seven men and 13 women, mean age 39 years, and 20 non-obese subjects, nine males and 11 females, mean age 38 years. we determined the plasma levels of malondialdehyde, stress an index, total antioxidant capacity, catalase, reduced and oxidized glutathione and inflammatory markers (c reactive protein and á-1 acid glycoprotein). in the obese group, these parameters were determined before and 2, 6 and 12 months after gastroplasty. results: preoperatively, the obese group showed elevated levels of inflammatory markers of oxidative stress (malondialdehyde levels and stress index) and lower levels of indicators of antioxidant defense compared to the control group. weight loss was accompanied by gradual reduction in the levels of malondialdehyde and stress index. we found an increased concentration of reduced glutathione and total antioxidant status and reduced levels of inflammatory markers. conclusion: weight loss improves the inflammatory state and oxidative stress levels.