The positive effects of bariatric surgery on weight loss and obesity-related co-morbidities are no longer doubted. In addition, these procedures can also be performed safely with low mortality and morbidity [
5,
12,
38]. The range of available bariatric procedures is tremendous [
7,
17,
39‐
45]. Almost every year, a “new” procedure is focussed upon within the scientific community [
18,
19]. However, there are only few RCTs comparing the two most commonly performed bariatric procedures, i.e. RYGB and SG with regard to actual weight loss and/or improvement of obesity-related co-morbidities in the mid- and long-term [
12,
15]. It is therefore impossible to advocate any particular, bariatric surgical method, because one still does not know which patient benefits most from which procedure. A systematic review revealed that the EWL after 24 months is not statistically different between RYGB and SG [
41]. In addition, the same publication demonstrated the poor data quality among publications dealing with SG. The urgent questions concerning comparisons between SG and the current gold standard of RYGB with respect to long-term EWL, course of obesity-related co-morbidities, course of GERD and QoL, are still not answered. In the last 2 years, however, a small number of RCTs were started with the goal of examining some of these issues [
12,
14,
15,
17,
39]. To our knowledge, the BariSurg trial will be the first multi-centre, randomized controlled patient and observer blind clinical trial with a sufficient sample size analyzing hard clinical endpoints such as mid- and long-term EWL, morbidity and mortality. In addition BariSurg will also answer some of the urgent questions associated with SG, such as course of obesity-related co-morbidities, dumping syndrome and GERD. Thus, BariSurg will contribute to class 1B evidence, which enable future class 1A evidence in form of meta-analyses. The remission of obesity-related co-morbidities, such as T2DM, following bariatric procedures is already known [
1‐
3,
40]. In particular, the RYGB has been considered as a potential therapy for T2DM, even in patients with a BMI of less than 35 kg/m
2 [
41,
42]. However, SG also has a significant impact on T2DM remission [
24,
43,
46]. Prior RCTs have suggested similar outcomes after RYGB and SG with regard to glucose metabolism [
15,
44,
47]. The incidence of GERD seems to be more frequent after SG whereas RYGB is considered a therapeutic option in patients with GERD [
15,
45,
48]. Nevertheless, the course of GERD after SG is controversial and definite evidence supporting either side does not exist [
23,
49,
50]. The current discussion among bariatric surgeons is almost unidirectional and focused on “hard” clinical facts such as weight loss, T2DM remission, and the course of other obesity-related co-morbidities. “Soft” clinical facts such as QoL have gained importance. At the present, there is few literature about patients’ expectation concerning surgical intervention. Data from the Michigan Bariatric Surgery Collaborative on a total of 8.847 patients showed an increased qoL after SG and RYGB [
51]. However long-term results of QoL after RYGB and SG are not available. The combined evaluation within this trial of the primary endpoint of EWL after 24 months plus the course of EWL, obesity-related co-morbidities, GERD, morbidity and mortality over 5 years, will lead to further insights of the pros and cons of both procedures. Additionally, the setting of this multi-centre, randomized trial enables a maximum reduction of bias and increases internal and external validity [
52].