We describe the sonographic findings in five pediatric patients with roundworm obstruction. All patients were referred with a clinical diagnosis of acute appendicitis. On ultrasonography (US), an individual worm, when viewed along its longitudinal axis, appeared as a hypoechoic tubular structure with well-defined, echogenic walls. Frequently, the individual body segments could be distinctly visualized. The alimentary canal of the worm was seen either as a single central echogenic line (when in a collapsed state) or as two parallel hyperechoic bands with a hypoechoic center (when distended). When examined transaxially, the individual worm resembled a target with its circular, echogenic body wall and its central dot-like alimentary canal. On prolonged scanning, the worms always showed curling movements. In two patients, a bolus of worms mixed with fecal matter and air produced an unusual appearance of a complex, echogenic mass (helminthoma). Although, an individual worm occasionally resembled an inflamed appendix, visualization of the alimentary canal and individual body segments along with its curling movements helped establish the correct diagnosis. All patients promptly responded to a hypertonic saline enema and no patient was subjected to surgery. Sonographic findings in roundworm obstruction are fairly characteristics to advocate the routine use of sonography for diagnosing this entity.