The Roux-en-Y procedure can be used after division of the jejunum at approximately 30 cm beyond the ligament of Treitz. With the jejunum held outside the abdomen, the arcades of blood vessels can be more clearly defined by transillumination with a portable light (Figure 16). Two or more arcades of blood vessels are divided and a short segment of devascularized intestine resected (Figure 17). The arm of the distal segment of jejunum is passed through the opening made in the mesocolon to the left of the middle colic vessels. Additional mesentery is divided if the end segment of the jejunum does not easily extend up to and parallel with the crus of the diaphragm behind the esophagus. When the adequate length has been assured, the decision must be made whether it is safer and easier to do an end-to-end anastomosis or an end to-side anastomosis with the esophagus. If the end-to-side anastomosis is selected, the end of the jejunum is closed with two layers of 0000 silk (Figures 18 and 19). The end of the jejunum is then pulled through the opening made in the mesocolon to the left of the middle colic vessels (Figure 20). Care must be taken to avoid angulating or twisting the mesentery of the jejunum as it is pulled through. The jejunal wall is anchored about the margins of the hole in the mesocolon. All openings in the mesocolon should be occluded to avoid the possibility of an internal hernia. The opening created beneath the free margin of the mesentery and the posterior parietes should be obliterated by interrupted sutures placed superficially, avoiding injury to blood vessels.