Roundworms migrating into the biliary tract are a relatively common cause of biliary symptoms in areas where the parasite is endemic. Visualization of worms by conventional radiologic methods is often unsatisfactory, whereas ultrasonography offers a rapid, safe, and noninvasive approach to the diagnosis. Using real-time ultrasonographic scanning we demonstrated for the first time the characteristic morphology of the worms in a patient with biliary ascariasis. In addition, the motility of the worms in the biliary tract could be confirmed. Ultrasonography is also a convenient method for the follow-up of patients. Endoscopic biliary drainage and instillation of piperazine citrate through a nasobiliary drain is a logical therapy and was used successfully in this patient.