Several studies conducted in the USA have demonstrated that the effectiveness of bariatric surgery differs between patients from African and European origin. However, little is known on differences in outcomes after bariatric surgery between individuals from other ethnic backgrounds. In this retrospective study, we found that, in terms of weight loss, gastric bypass surgery is less effective in African, South Asian, Turkish and Moroccan patients than in their ethnic Dutch counterparts. Our results underscore that ethnic differences in the effectiveness of bariatric surgery are not limited to those between patients of African and European origin, but extend to other minority groups as well. Therefore, it is important that prospective studies both determine ethnic differences in weight loss-related improvement of co-morbidities and elucidate the exact reasons for these ethnic disparities.