Seventy-five patients underwent a 90 percent distal gastric bypass for morbid obesity. The average weight was 121.4 kilogram, height 164 centimeters, and age 31.4 years in these 70 women and five men. There was a total of 20 surgical complications in the 75 patients, with wound infection being the most common. Sixteen chronic complications were noted and consisted of vomiting, diarrhea, reflux esophagitis, dysphagia, and vitamin deficiencies. None of the above complications were life-threatening or required dismantling of the bypass. Of 54 patients followed for 12 months or more after gastric bypass, there was a 24.5 percent average weight decrease at 6 months, and this progressed to 35.8 percent by 12 months. Fifty-two patients undergoing small bowel bypass previously at the same institution had a 25.4 percent weight reduction at 12 months. Of 54 patients, 83 percent followed for one or more years after gastric bypass have had an excellent or good clinical result, whereas only 42 percent of the 52 patients undergoing small bowel bypass have had an excellent or good clinical result with the same criteria. It is concluded that the Mason 90 percent distal gastric bypass is a suitable form of surgical treatment for the morbidity obese patient who cannot lose weight by dietary measures.