Utero-rectal sink is a normal physiological anatomical structure that is not a serious problem. It refers to the peritoneal junction between the uterus and the rectum of the woman, which is at its lowest point. There is a thin mucosal layer between the utero-rectal sulcus and the posterior vaginal fornix of the woman. When a woman has an intra-abdominal fluid collection, it is usually stored in the recto-uterine recess. When a woman has pelvic inflammatory disease or a ruptured tubal pregnancy, the fluid collection in the recto-uterine recess may increase. Therefore, fluid can be aspirated from the retrovaginal vault to clarify the amount of bleeding and inflammatory infection to assist in clinical diagnosis. Normally, the front of the uterus is adjacent to the bladder and the back is adjacent to the rectum. Between the uterus and the bladder is covered by the anterior peritoneum, while between the uterus and the rectum is covered by the posterior peritoneum, also known as the utero-rectal sink.