As urologic surgery becomes more extensive planned or inadvertent compromise of the vascular supply of the bowel becomes more likely. Familiarity with the normal anatomy of the vascular supply of the large and small intestines must, therefore, be part of every urologist's fund of knowledge. With an appreciation of the critical areas of collateral circulation conclusions can be drawn as to which arteries can and cannot be ligated safely. Intraoperative Doppler flow studies may help the surgeon to evaluate whether collateral supply is adequate to maintain bowel viability. In certain marginal situations hydration and postoperative treatment with antibiotics may be helpful.