A 4cm cyst on the right side of the uterus is not serious if it has no obvious symptoms and is mostly physiologic, but if it grows faster and is pathologic in nature, it may lead to serious symptoms, complications, and so on. Uterine adnexal cysts include ovarian cysts and tubal cysts, and according to the nature of the cysts, they can be divided into physiological cysts and pathological cysts. Physiological cysts are mainly related to the development of menstrual cycle and will disappear within 1~3 months; pathological cysts are related to diseases and need to be treated according to the condition. Causes of pathologic cysts include endocrine disorders, pelvic infections, abnormal follicular function, abnormal corpus luteum function, and endometriosis. Most cysts have no obvious symptoms when they are small in size. When their diameter is larger than 5cm, they may show symptoms such as lower abdominal pain, cramping sensation, pain during sexual intercourse, and irregular vaginal bleeding. If the cyst continues to develop with faster growth rate, corresponding clinical symptoms and untreated, it may also lead to more serious consequences such as cyst torsion, cyst rupture, cyst bleeding and cyst malignancy. Therefore, it is recommended that even people with small cysts and no obvious symptoms of adnexal cysts should consult a doctor in a timely manner to clarify the nature of the cysts and the causes of the cysts, and then closely observe their development and undergo active and regular treatment.