Obesity is currently one of the greatest global health problems. It is associated with increased morbidity and mortality, worsened quality of life (QOL) and significant health care costs. For morbidly obese patients, bariatric surgery is the only effective treatment option showing good and sustainable long-term weight loss and remission or improvement of obesity related comorbidities. Laparoscopic Roux-en-Y gastric bypass (LRYGB) is the gold standard of bariatric surgery with demonstrated longterm efficacy. During the last years, laparoscopic sleeve gastrectomy (LSG) has become the most common bariatric procedure despite the lack of long-term followup results at that time.

The main aim of this thesis was to compare the short and long-term outcomes on weight loss, obesity related co-morbidities, and QOL after LSG and LRYGB in the treatment of morbid obesity in a randomized clinical multicenter equivalence trial (SLEEVEPASS). In addition, this thesis aimed to assess the QOL improvement after laparoscopic gastric banding (LGB) and to compare it with the QOL of the general population.

The operative time of LSG was shorter with no difference in early (30 days) overall morbidity between LSG and LRYGB. At 5-year follow-up, the primary endpoint of percent excess weight loss (%EWL) was 57% after LRYGB and 49% after LSG. The mean difference was not statistically significant based on the prespecified equivalence margins. At 5 years, there were no differences regarding the long-term resolution of type 2 diabetes or dyslipidemia, improvement of QOL, morbidity, and mortality, but hypertension resolution was superior after LRYGB. QOL improved significantly after LAGB and was maintained at five-year follow-up but did not reach the level of the general population.