Comparison of participants in a randomised controlled trial (RCT) with observational data from patients operated in Sweden during the same period of time. The primary objective is to compare effects from a complex surgical intervention from RCT and observational data.

Randomised controlled trials (RCT) are "golden standard" for assessing interventions in medical science. Due to ethical or practical reasons, RCTs may however not always be feasible. The study objective was to test if the results from the RCT differ from observational data in a setting with a complex surgical intervention.

Using the Scandinavian Obesity Surgery Registry database we intend to compare patients operated with laparoscopic gastric bypass surgery within a register based RCT from May 1st 2010 until Nov 14th 2011, with all patients operated with the same procedure registered in the database during the same period of time.

Primary end-point measures are severe complications within 30 days (safety outcome) and surgery for small bowel obstruction (efficacy outcome) within 4 years.

Inclusion Criteria:

• The same as acceptance criteria for bariatric surgery according to the 1991 NIH Consensus Statement

Exclusion Criteria:

• retrocolic gastric bypass procedure
• previous bariatric procedures
• primary open procedures
• missing data on handling of the mesenteric defects

Group data will be published. Deidentified individual participant data for all primary and secondary outcomes will be available after study completion.