Postoperative ascites is a rare and serious complication of laparoscopic procedures. Urinary tract injury, bowel injury, and lymph duct injury are the common causes; however, in some patients no definitive cause can be identified after an extensive diagnostic work-up. We present a case of postoperative ascites of unknown origin. The patient recovered with general treatments. We presume that diffuse peritoneal injury may have been caused by unidentified substances in our patient.