Ischemic colitis, a condition of middle-aged to elderly patients, occurs uncommonly in younger persons. In this study, we describe the clinical and pathological features of 18 young adults (mean age, 29 years; age range, 17-39 years) with spontaneous ischemic colitis, 17 of whom were women. All presented with abrupt onset of severe, cramping abdominal pain followed by hematochezia. Colonoscopic visualization of the mucosa showed segmental hyperemia, friability, and erosion affecting the distal transverse colon (three cases), splenic flexure (three cases), descending colon (five cases), and sigmoid (seven cases). Mucosal biopsy documented superficial ischemic necrosis in seven patients; 11 patients had full-thickness mucosal necrosis with regeneration. Colonic mucosa proximal and distal to the ischemic segment was endoscopically normal in all patients and histologically normal in the eight patients in whom biopsies were obtained. All patients recovered with supportive care. Median duration of illness was 2.1 days (range, 1-4 days). Ten women (59%) were using low-dose estrogenic oral contraceptive agents, compared with the 1988 national average of 18.5% oral contraceptive users among females aged 15 to 44 years. The calculated odds ratio yielded a greater than sixfold relative risk for the occurrence of ischemic colitis among oral contraceptive users. In addition, four women not currently on hormonal contraceptive therapy had a past history of oral contraceptive use; the three remaining women were taking estrogen as replacement therapy after oophorectomy. In one patient, documented reversible ischemic colitis recurred on resumption of oral contraceptive use; four women reported symptoms and signs of recurrent ischemia but did not seek further medical evaluation. Our data indicate that transient colonic ischemia represents a form of acute segmental colitis in young adults; before the 5th decade of life, spontaneous ischemic colitis is a disorder found almost exclusively in women and is associated with the clinical use of exogenous estrogenic agents.