A man of 57 suffering from nephroureterolithiasis was treated by ESWL (6 sessions) both in the prone and supine positions. Several hours after the last treatment (prone position) the patient complained about increasing abdominal pain which we found to be caused by an intra-abdominal perforation. In an emergency laparotomy we detected a perforation on the ventral wall of a small bowel loop, which was fixed at the colon ascendens on the rear side. Histological examination provided no evidence of previously existing intestinal disease. Thus, we suggest that this case is a rare major complication of ESWL.