The epididymis consists of a highly convoluted epididymal duct, which can be 4 to 6 meters long when straightened. It has the function of storing and discharging sperm, promoting sperm maturation and secreting fluid for sperm nutrition. Epididymal cysts are not uncommon in male medicine and urology, and their incidence increases with age, and it is very common for men after the age of 40 to have epididymal cysts. An epididymal cyst is actually a swelling filled with colorless fluid, the size of a pea or a golf ball, and can remain unchanged in size for a long time. Cysts are usually found at the head and tail of the epididymis, and are more common unilaterally than bilaterally. There are several conditions for the formation of epididymal cysts: the residual tissues from the embryonic period are complicated by cysts with clarified fluid in the sac; some of the epididymal ducts or vas deferens are blocked, resulting in the formation of cysts due to the obstruction of fluid and sperm discharge from the epididymal ducts, the contents of which are seminal fluid; cysts are formed after inflammation of the epididymis. Epididymal cysts usually have no symptoms, and patients often discover them unintentionally when bathing. If there are symptoms such as pain, rapid enlargement of the cyst, redness of the scrotal skin and pressure at the root of the penis, it may be a combination of inflammation. Epididymal cysts mainly have serious effects on infertile men. If they occur on one side of the epididymis, they are not so bad as to cause azoospermia, but if they occur on both sides, or if they occur on one side and combine with sperm production dysfunction of the other testicle, they may cause azoospermia. Epididymal cyst is a benign lesion and will not become cancerous, so there is no need to make a fuss about it. If the cyst is small, it usually does not need to be treated. If it appears to increase in size or has an annoying discomfort, surgery can be considered. Of course, it is important to consider whether the patient has already had children and to assess whether the surgery will cause sequelae such as obstructive azoospermia. Surgical treatment is relatively simple and does not take long. Cystectomy is possible if the cyst is localized, and epididymoidectomy is required if the cyst affects the whole epididymis. Since testicular masses can occur in many diseases, it cannot be assumed that painless cysts are epididymal cysts, such as testicular tumors and inflammatory nodules in the epididymis, which may also be asymptomatic. Therefore, when a lump is found in the scrotum, even if it is not painful or itchy, it should be examined by a doctor. Usually, after scrotal examination, the doctor can initially determine the nature of the epididymal cyst. Transillumination test is a simple examination method because light can penetrate a fluid-filled cyst but not a substantial mass, so the transillumination examination method can distinguish between cysts and substantial lesions, but for epididymal cysts with dense cyst wall tissue or high cyst tension, they must be identified with epididymal tumors, chronic epididymitis, and epididymal ossification, etc. Ultrasound examination is the most commonly used examination method.