Chylous ascites is the pathologic accumulation of chylous fluid in the peritoneal cavity, caused by lymphomas, metastatic malignancies, and abdominal surgeries, rarely due to surgical trauma of the cisterna chyli or its major branches. A 24-year-old man with history of Marfan syndrome presented to our hospital with abdominal distention, abdominal pain, fluid in the incision region, and weakness. He had underwent an elective open aneurysm repair surgery nine days before for thoracoabdominal aortic aneurysm. Computed tomography revealed massive fluid collection in the abdominal cavity, which was drained surgically. He was diagnosed with chylous ascites and was discharged after conservative treatment.