Endometriosis with ascites is a rare clinical presentation. We describe a case of a 39-year-old nulliparous woman who presented with hypogastric pain. Laboratory analysis showed an elevation of CA-125 and CA19-9 serum concentrations. Pelvic ultrasound revealed an ovarian mass and free peritoneal fluid confirmed by computed tomography. The patient underwent exploratory laparotomy which revealed a large amount of chocolate-like liquid material in the peritoneal cavity. In the right ovary resected an encapsulated mass. Histologic examination confirmed endometrioma diagnosis. Endometriosis should be considered in the differential diagnosis in women of childbearing age presenting with ascites.