Two cases of obstruction of the bypassed small intestine after jejunoileal shunt for obesity are presented. These cases illustrate the possible failure of radiologic visualization of the obstructed bowel since no gas traverses this bowel, as well as two of the possible causes-internal herniation and volvulus. A third cause, intussusception of the blind loop into the colon, has been reported. Obstruction of the bypassed bowel demands surgical intervention and could lead to perforation and peritonitis if untreated. Its prevention involves the closure of all mesenteric defects at the original operation. Surgeons should be aware of the possibility of these conditions in any patient who has had a small-bowel bypass operation.