During routine transabdominal ultrasonography of the hepatobiliary tract an occasional persistent bright linear or concave echo was detected that disrupted the normal images we routinely obtained of the pancreatic head. We began to suspect this echo to be the sonographic representation of a duodenal diverticulum. To confirm our suspicions we performed a prospective study. Over a 20 month period, 30 consecutive patients with a sonographically suspected duodenal diverticulum were followed up with either an upper gastrointestinal series, gastroscopy, or, depending on the patient's clinical symptoms, endoscopic retrograde cholangiopancreaticography. One patient was examined with simultaneous fluoroscopy and ultrasonography. The results of these examinations were then compared to the respective ultrasonograms by a qualified radiologist and sonographer. The suspected duodenal diverticulum, detected primarily with ultrasonography, was confirmed with follow-up examinations in all 30 patients. The persistent echo detected sonographically had the same anatomic position as the diverticulum seen during fluoroscopy. We concluded that duodenal diverticulum located near the pancreatic head has a rather typical sonographic appearance.