The purpose of this study on adolescents between 13 and 18 years of age with morbid obesity is to determine whether surgical treatment gives more health benefits than standard conservative treatment, and if laparoscopic gastric bypass is a method with high safety and a low complication rate.

The study has two intervention arms:

Experimental: Group A Surgery; laparoscopic gastric bypass

Active comparator: Group B Patients from Child Obesity Registry of Vestfold who get standard conservative treatment in a multidisiplinary team at Morbid Obesity Center.

All patients are referred to Morbid Obesity Center from other hospitals or general practionairs in Norway. The procedure will take place at the Vestfold Hospital Trust The participants are included for 2 years follow-up with visits to a multidisciplinary team every 3rd month at the Morbid Obesity Center. Total follow-up time is ten years.

Inclusion Criteria:

• Between 13 and 18 years of age at inclusion
• Tanner stage 4-5
• BMI > 40 kg/m2 or BMI > 35 with at least one comorbidity (type 2-diabetes, obstructive sleep apnea, serious hypertension or cerebral pseudotumor)
• At least one year multidisciplinary treatment completed

Exclusion Criteria:

• Tanner stage < 4
• Substantial risk for lack of compliance
• Obesity syndrome (e.g., Prader Willi syndrome)
• Obesity related to brain damage
• Serious general disease
• Monogenic obesity