Mirror image transposition of abdominal and thoracic viscera is termed situs inversus. Duodenal obstruction in situs inversus is rare. A preduodenal portal vein, though not uncommon in situs inversus, rarely causes duodenal obstruction. Where obstruction by a preduodenal portal vein is diagnosed, a duodeno-duodenostomy is the recommended treatment. A duodenal diaphragm and other more common causes of duodenal obstruction should also be excluded in these patients.