Patients with a BMI of greater than 35 who have serious medical problems such as sleep apnea, that would improve with weight loss. A study done in Sweden compared the rates of diabetes and hypertension in two groups of obese patients - those who underwent surgery and those who didn't. Each group had similar body weight at baseline (the start of the study). At 2 years, diabetes and high blood pressure were lower in the surgery treated patients.

Surgical procedures of the upper gastrointestinal tract are collectively called bariatric surgery. The initial surgeries performed were the jejunocolic bypass and the jejunoileal bypass (where the small bowel is diverted to the large bowel, bypassing a lot of the surface area where food would have been absorbed). These procedures were fraught with problems and are no longer performed. Currently, procedures used include making the stomach area smaller or bypassing the stomach completely.

In the cases of making the stomach smaller, vertically banded gastroplasty is the most common procedure, where the esophagus is banded early in the stomach. The other procedure is gastric banding, where an inflatable pouch causes gastric constriction. Changing the volume in the ring that encircles the stomach can change the amount of constriction. Gastric bypass essentially causes weight loss by bypassing the stomach.

The risks of surgery include the usual complications of infection, blood clots in the lower extremities and in the lungs, and anesthesia risk. Specific long-term risks related to obesity surgery include lack of iron absorption and iron deficiency anemia. Vitamin B 12 deficiency can also develop and could lead to nerve damage (neuropathies). Rapid weight loss may also be associated with gallstones.