Interstitial cells of Cajal (ICC) are fundamental regulators of GI motility. Here, we report the manometrical abnormalities and abnormalities of ICC distribution and ultrastructure encountered in a 30-yr-old patient with megaduodenum and pseudo-obstruction. Full thickness biopsies taken during laparoscopic placement of a jejunostomy showed vacuolated myocytes and fibrosis predominantly in the outer third of the circular muscle layer of the duodenum, suggestive for visceral myopathy. The distribution of ICC was also strikingly abnormal: by light microscopy, ICC surrounding the myenteric plexus were lacking in the megaduodenum, whereas ICC were normally present in the duodenal circular muscle and in the jejunum. By electron microscopy, very few ICC were identified around the duodenal myenteric plexus. These findings suggest that abnormalities in ICC may contribute to the disturbed motility in some myopathic forms of intestinal pseudo-obstruction.