This paper refers to 50 unusual cases of 542 consecutive adult patients who underwent surgery because of acute intestinal obstruction. Of the 38 small bowel cases, 5 were caused by hernias in anomalous recesses (1 prevesical, 2 left paraduodenal, and 2 paracecal hernias), 6 by a gallstone ileus, 14 to the presence of a bezoar or foreign body, 8 to extended postradiation perivisceritis, 3 to Meckel diverticulum volvulus, 1 to transepiploic hernia, and 1 to ileus-Meckel hematoma during anticoagulation treatment. The 12 large bowel cases included 3 diaphragmatic hernias (1 late post-trauma), 3 cases of colo-colic intussusception, 1 case of obstructive cholecystitis, and 5 cases of Ogilvie's syndrome. Major technical problems have to be immediately solved in the case of left paraduodenal, prevesical, or diaphragmatic hernias; however, during laparotomy, there may also be some difficult and unpredictable problems caused by widespread postradiation perivisceritis.