Chylous ascites is the extravasation into the peritoneal cavity of milky chyle that is rich in triglycerides. Sixty to seventy percent of chylous ascites cases are caused by cirrhotic liver disease, congestive heart failure, or malignancy. The most common malignancy associated with chylous ascites is lymphoma. Rarely, tuberculosis has been reported as a cause of chylous ascites. Appropriately, lymphoma, ovarian cancer or tuberculosis is considered first in the differential diagnosis when a young woman of reproductive age presents with chylous ascites. Recently, we examined a 26-year-old woman who visited our hospital because of abdominal distension. Ascites tapping, esophagogastroduodenoscopy, colonoscopy and diagnostic laparoscopic biopsy led to a diagnosis of intraperitoneal endometriosis with chylous ascites. To date, some cases of endometriosis complicated by massive ascites have been reported. However, endometriosis complicated by chylous ascites has not been previously reported. The case was successfully treated using a gonadotropin-releasing hormone agonist and diuretics. (Korean J Gastrointest Endosc 2010;41:368-372)