The Gastric Bypass is the most commonly performed Weight Loss Surgery procedure in
the United States at this time. 
The Gastric Bypass is almost always done laparoscopically in my practice.

Full Description of The Procedure

During surgery, we use a surgical stapling device to divide the upper stomach and create a tiny stomach "pouch" at the upper end. This pouch is shaped to be about the size of your thumb, and will hold 15 ml or less.  In other words, the new stomach pouch is even smaller than a shot glass. This means that 2-3 tiny bites of food is all a patient can hold, and this restriction on the amount of food eaten is the main way that the Gastric Bypass promotes weight loss.
Food leaves this tiny stomach pouch into a segment of small intestine (the Roux limb) which is brought up from the mid-abdomen and is surgically attached to the stomach pouch. A key feature of this small intestine (medical name is "jejunum") is that it cannot handle concentrated calories. If the patient consumes foods that contains sugar or fat (ice cream or M&M's would be classic "no-no's") this segment of intestine reacts by creating a temporary illness called dumping syndrome.
Dumping syndrome can be caused after gastric bypass by intake of simple carbohydrates (sugar, or some starches). Dumping syndrome is characterized by palpitations (fast heart rate), a clammy feeling, queasiness and nausea, sometimes vomiting, and sometimes diarrhea. Usually the patient feels weak, and must lie down for 30-60 minutes. Dumping syndrome is not dangerous but it feels absolutely horrible.  For best weight loss patients should stay away from sugar and other carbohydrates - the thought of dumping syndrome seems to help change habits away from these types of food.