Three-year-old male child testicles on both sides of the size is not the same, if the difference is relatively small, is a normal phenomenon, if the difference is large, may be syringomyelia, cryptorchidism, testicular tumors, etc. caused. 1. Syringomyelia: it refers to the congenital peritoneal syringomyelia that is not closed, resulting in the fluid in the abdominal cavity flowing out through the unclosed syringomyelia and accumulating in the syringomyelia lumen inside the scrotum, and the scrotum on the affected side has a significant increase in size. 2. Cryptorchidism: if the child is affected by endocrine abnormality, testicular development abnormality, structural abnormality, genetic factors, etc., it will lead to different sizes of testicles on both sides of the three-year-old baby boy, and the affected child mainly manifests as the flattening and deflating of the scrotum on the affected side, and there is no self-consciousness and discomfort usually. 3. Testicular tumor: three-year-old boy’s testicles are not the same size on both sides of the testicles may be caused by testicular tumors, mainly related to physical and chemical injuries, hormone metabolism disorders and infections, etc., the child’s scrotum can be touched by painless lumps, or feel the scrotum dull pain, lower abdominal swelling and other discomforts. Parents are advised to bring their children to regular hospitals in time, and under the diagnosis of the doctor, adopt targeted treatment according to the specific condition of the children.