Ischemic changes in the colon that progress to gangrene present diagnostic and therapeutic difficulties associated with poor survival. During the past 10 years, 36 patients with colonic ischemia were treated. Two clinical groups were evident. The spontaneous ischemic colitis group (type I) included 17 patients who were well before the onset of gastrointestinal symptoms. The cause of type I ischemic colitis is not apparent; it is attributed to occlusive or nonocclusive ischemia. The other group (type II) included 19 patients who developed ischemia of the colon associated with shock secondary to various disease processes. Radiographic evidence of distended bowel correlated well with full-thickness necrosis as determined clinically or pathologically. Twenty-one patients died, for a mortality rate of 58 percent. While full-thickness gangrene was fatal in 71 percent of the patients, mucosal necrosis only was associated with an 88 percent survival rate. The results of treatment should improve with an increased awareness of ischemic colitis, earlier appropriate operative intervention, and more appropriate use of ileostomy and colostomy.