On examination, he was extremely thin and weak, but there were no other abnormal physical signs.Investigations showed a moderate hypokalaemic alkalosis and a blood urea of 22.8 mmol/litre. The barium meal showed obstruction of the third part of the duodenum with proximal dilatation (Fig. 1).The differential diagnosis was thought to include superior mesenteric artery syndrome (SMAS), small bowel lymphoma, external compression from an abnormal band, annular pancreas or intraduodenal diverticulum. After adequate rehydration and correction of the metabolic disturbances, a laparotomy was performed. The first and second parts of the duodenum were dilated and hypertrophied but there was no other abnormality. Their dilatation came to an abrupt end where the superior mesenteric vessels crossed the third part of the duodenum. Duodenotomy excluded an intraduodenal abnormality. It was concluded that this was a case of superior mesenteric artery syndrome and a short looped, retrocolic duodenojejunostomy was fashioned (Fig. 2)