In order to find out the etiological patterns of intestinal obstruction, we reviewed 1205 cases diagnosed as intestinal obstruction at our hospital. The operative findings, locations of obstruction and pathological results were analyzed among 707 cases who were operated on. The most common cause of colon obstruction was tumor (78.7%). The etiologies of small intestinal obstruction were: adhesions, 47.4%; hernia, 22.1%; tumor, 11.8%; intussusception, 8.8%; foreign bodies, 3.7%; and miscellaneous causes, 6.2%. In the patients older than 40 years, the most common causes of intestinal obstruction were adhesion and malignancy, in contrast to hernia and intussusception that were commonly found in children. The mean age of the patients with colon obstruction was older than those with small bowel obstruction, 55.7 +/- 21. vs 39.4 +/- 17.3 (P less than 0.001). Of the patients with previous abdominal surgery, adhesions caused the obstruction in up to 60.5%. Among the 102 cases who had been operated for abdominal malignancy, the cause of intestinal obstruction was due to recurrent tumor in 78 patients (76.4%). Of patients without previous abdominal surgery, the etiologies of intestinal obstruction were: incarcerated hernia, 36.7%; tumor, 21.1%; intussusception, 15.6%; and adhesion, 13.8%. The incidence of strangulation obstruction was 25.7%, of which the major causes were adhesions, 51.7%; and hernia. 43.0%. We concluded that the most common cause of colon obstruction was tumor. The two most common causes of small intestinal obstruction were adhesions and hernia. Age and past history of abdominal surgery can much help for the differential diagnosis.