In gynecology clinics, patients often come to the clinic with a diagnosis of “pelvic effusion” on ultrasound, but most of them often have no symptoms and look nervous. Is pelvic effusion a disease? Does it need to be treated? The peritoneal cavity contains intestinal tubes, omentum, uterus, fallopian tubes, ovaries, liver and other organs, which are intraperitoneal organs. The peritoneum covers the abdominal organs and the surface of the pelvis and abdominal cavity, and the peritoneum can leak a small amount of fluid, called peritoneal leakage fluid. Leaky fluid is mostly yellowish, thin and transparent, which can prevent the organs in the peritoneal cavity from adhering to each other to play a lubricating role in intestinal peristalsis. Under normal conditions, the peritoneal leakage fluid is usually less than 200 ml. The pelvic cavity is part of the peritoneal cavity and is in a low position when standing and the rectal recess of the uterus is in the lowest position of the peritoneal cavity when lying down. Therefore, a dark area of fluid is visible in the rectal recess of the uterus on ultrasound, which is also known as pelvic fluid. At the time of ovulation, the amount of fluid may increase due to the discharge of follicular fluid and the oozing of blood from the ovulation incision, and sometimes ovulation may even be seen on ultrasound again, when the amount of pelvic fluid may increase. This leakage of peritoneal fluid as well as follicular fluid from ovulation can lead to pelvic effusion, which is a normal physiological phenomenon and does not require treatment. The pelvic fluid, which is often seen in gynecological clinics as a result of ultrasound, is actually a normal physiological phenomenon and does not need to be treated. However, there are five conditions worth noting: (1) When there is pelvic inflammatory disease, the peritoneum is stimulated by inflammatory substances, which can produce a large amount of exudate, and the ultrasound examination also produces “pelvic fluid”, but at this time is often accompanied by fever and other symptoms of infection, blood tests, such as white blood cells can be changed. (2) When the amount of free fluid in the abdominal cavity exceeds 200ml due to cirrhosis complicated by increased portal vein pressure, dilated visceral arteries, reduced plasma colloid osmotic pressure and other factors, it is called “ascites”. (3) When suffering from abdominal tumor, the peritoneum is stimulated by inflammatory substances and so on, which can produce a large amount of exudate, and ultrasound examination also has “pelvic fluid”, which often has the clinical manifestation of the primary tumor. (4) In ectopic pregnancy, the local tissue of the lesion will rupture and bleed, and there will be “pelvic fluid” on ultrasonography. The patient often has a history of menopause, and may be accompanied by strong pain of peritoneal irritation and nausea and vomiting, etc. If there is a large amount of bleeding, it may be accompanied by dizziness and other shock symptoms. (5) Occasionally, there may be bleeding from the ruptured follicle during normal ovulation, or the rupture of the corpus luteum and bleeding after ovulation in the later part of the menstrual cycle, with symptoms such as vague pain in the abdomen and “pelvic fluid” on ultrasonography. However, if the rupture is bleeding heavily, it will cause symptoms similar to ectopic pregnancy, and at this time, there may be more pelvic fluid on ultrasound, which is a pathological condition and should be seen by a doctor. The above five pathological conditions need to be seen by a doctor promptly and treated in an emergency if necessary.