The objective of this retrospective study was to identify the ability of preoperative endoscopy of the lower gastrointestinal tract and other tests to predict large bowel resection in patients with an adnexal mass. We reviewed 573 patients with a suspected adnexal mass admitted for surgery between 1987 and 1997. Two hundred fifty four patients (44%) had preoperative sigmoidoscopy (n= 97) or colonoscopy (n= 157). We identified patients who underwent a colorectal operation as part of their surgery and correlated surgical findings with the results of preoperative endoscopy, preexisting clinical symptoms, preoperative pelvic exam and ultrasonography, and the CA125 level. The sensitivity and positive predictive value of bowel endoscopy for predicting large bowel surgery were 18% and 59%, respectively. Multivariate analysis showed preexisting bowel-related symptoms, a pelvic exam suggestive of malignancy, a CA125 value > 1000 U/ml, and infiltration of the colorectal wall at bowel endoscopy to be independently associated with subsequent colorectal surgery. We conclude that preoperative bowel endoscopy cannot accurately predict colon resection in patients with a suspected adnexal mass. Preexisting bowel-related symptoms, a pelvic exam suggestive of malignancy and a CA125 value > 1000 U/ml are associated with subsequent colorectal surgery.