We evaluated the preoperative determination of the etiology and effectiveness of the diagnostic modalities, as well as the incidence of various causes of intestinal obstruction (IO) from 1981 through 2001 at a university-affiliated emergency center. Patients with a history of prior laparotomy or evidence of hernia on physical examinations were excluded. Eighty-three patients with surgically or endoscopically proven IO were reviewed. The most common cause of IO in the group with enteric obstruction was hernia while that in the group of colonic obstruction was carcinoma. Of the first preoperative diagnostic modalities to correctly determine the cause of obstruction, the most common were contrast enema and colonoscopy. Preoperative determination of the etiology was possible in 67% of the patients and was significantly more common in patients with colonic obstruction than in those with enteric obstruction.