PURPOSE Dumping is currently seen as a negative side effect of Roux-en-Y gastric bypass (RYGB). However, it may help patients to comply with their prescribed diet. In this study, we assess the role of dumping on weight loss in patients who have undergone conversion of failed restrictive surgery into RYGB. METHODS An analysis was performed of 100 consecutive patients who underwent revisional RYGB (rRYGB) between 2006 and 2011 due to inadequate weight loss or band intolerance after laparoscopic adjustable gastric banding (LAGB). The percentage of excess weight loss (%EWL) was used to evaluate weight reduction. The Sigstad clinical diagnostic index was used to detect dumping symptoms. RESULTS Fifty-five patients (59.1%) suffered from dumping. Overall, dumpers showed a greater %EWL than non-dumpers (83.8 ± 48.0 vs 66.9 ± 44.1%, respectively, p = 0.0725). When rRYGB was performed because of inadequate weight loss following LAGB, dumping played a crucial role in weight loss (88.0 ± 21.2 vs 68.9 ± 34.5%, p = 0.0137). This effect positively correlates to post-LAGB body mass index (BMI) with a statistically significant result at BMI > 35 kg/m2 (82.4 ± 15.7 vs 58.4 ± 32.4%, p = 0.00341). A regression analysis of the Sigstad dumping score and %EWL shows that dumping tends to increase the %EWL. CONCLUSIONS This study provides new insights into the effect of dumping on weight loss in patients who underwent conversion of failed restrictive surgery into RYGB. Based on the findings in our patient group, we suggest that dumping helps patients achieve sustainable weight loss. Therefore, dumping can be regarded as a positive side effect rather than a complication.