Retroperitoneal duodenal rupture is rare and is often difficult to diagnose on the plain abdominal x-ray. From a review of the lain abdomen films of 21 cases with retroperitoneal duodenal rupture, confirmed by operation, pneumoretroperitoneum was revealed in 16 cases; Air in the peritoneum was manifested as a bubby shadow in 12 cases, a renal halo in 9 cases, air shadow along the right psoas margin in 2 cases, air along the diaphragmatic crus in 2 cases and air in the right properitoneal fat in 2 cases, US and CT also revealed air bubbles and fluid collection around the right kidney. We recommend the plain abdomen as a useful diagnostic method for detection of pneumoretroperitoneum.