A healthy young woman with massive hemorrhagic ascites.

Retrograde menstruation is the backward movement of menstrual fluids. The underlying mechanisms remain unknown. The converse current itself is benign, but the result can be abdominal pain caused by peritoneal irritation and, eventually, endometriosis. The case was of a 25-year-old woman with lower abdominal pain accompanied by significant hemoperitoneum. Physical examination and inspection using abdominal ultrasonography and computed tomography failed to reveal a differential diagnosis. Detailed history taking revealed sexual activities during her menstrual period, which allowed for a diagnosis of retrograde menstruation. These findings emphasize the importance of extensive history taking.