INTRODUCTION: Obstructive jaundice is uncommon during childhood. Among the most common causes are congenital malformations of the pancreatobiliary tree. Transabdominal Ultrasound (TUS) and CT are of limited value in these disorders. ERCP has been the preoperative method of choice but is usually limited to major referral centers and has a relatively high morbidity. In adults, Endoscopic Ultrasound (EUS) has been used to evaluate obstructive jaundice. However, because of the size of echoendoscopes, the use of EUS in pediatrics has been limited to larger children. Alternatively, ultrasonic miniprobes can be passed through the 2.8 mm biopsy channel of a thin videoendoscope for use in smaller children. We describe the use of an ultrasonic miniprobe to help define the cause of obstructive jaundice in a three year old. CASE SUMMARY: A 35 month, 12 kg girl presented with jaundice (total bilirubin 6.6 mg/dl, alkaline phosphatase 471 IU/L) and pancreatitis (amylase 569 IU/L). TUS showed a markedly dilated 10 mm common bile duct (CBD). CT revealed CBD and intrahepatic duct dilation but no masses. To preoperatively define the patient's pancreatobiliary anatomy, we performed EUS using a Pentax EG- 2930 videoendoscope (outer diameter 9.8 mm) with a 12 MHz Olympus UM-2R ultrasonic miniprobe placed through the 2.8 mm biopsy channel into a water-filled duodenum. She was intubated for the procedure and was sedated with propofol. Because of the patient's small size, the miniprobe was able to visualize all the porta hepatis and pancreatic head. Miniprobe EUS showed a thick-walled 7 mm CBD which tapered down to a short narrowed segment about 2 cm proximal to the ampulla. No masses, stones or cysts were seen. EUS did demonstrate an anomalous junction of the pancreatic duct with the intrapancreatic portion of the CBD. The gallbladder had no stones and was thick-walled. Based on this information, the patient was explored. Intraoperative cholangiogram (IOC) confirmed the EUS findings. In addition, the IOC demonstrated an anomalous connection of the cystic duct into the right hepatic duct, a finding that was out of the range of view on EUS. A Roux-en-Y choledochojejunostomy with cholecystectomy was performed and the patient made an uneventful recovery. CONCLUSION: EUS can be successfully performed using an ultrasonic miniprobe passed through the 2.8 mm channel of a thin endoscope in relatively small children. As seen in adults, the high quality endosonographic images can be valuable in the evaluation of the pediatric patient with obstructive jaundice.