OBJECTIVE Certain factors in a patient's history, such as prior abdominal surgery or complicated diverticular disease, have been reported to hinder cecal intubation during colonoscopy. Over a 16-month period, 1,047 consecutive colonoscopies were prospectively evaluated to determine whether these factors were indeed clinically relevant. RESULTS Of the 90 patients (9 percent) who had incomplete intubation of the colon, there were significantly more women (66 percent) than men (34 percent) (P < 0.001). Women with a history of abdominal hysterectomy had a significantly lower cecal intubation rate (P < 0.01). A history of diverticulitis did not alter the cecal intubation rate. In patients with incomplete colonic intubation, the most proximal extent of intubation was the sigmoid colon in women (31 percent) and the right colon in men (68 percent). Sixty-seven percent of patients with incomplete intubation of the colon had a prior colonoscopy completed to the cecum (67 percent women, 67 percent men), whereas 50 percent had a follow-up colonoscopy completed to the cecum (56 percent women, 40 percent men). CONCLUSIONS Women, especially those with a history of abdominal hysterectomy, had a significantly lower cecal intubation rate usually because of an impassable sigmoid colon. Prior inability to complete colonoscopy to the cecum does not necessarily forecast future failure.