Generally 12 years old happens to be in puberty. Before the age of 12, the testicles of boys are in a relatively stationary phase, and after entering puberty they will rapidly increase in size, while the normal size of the testicles of 12-year-old boys is still inconclusive and can vary individually depending on the time of development and nutritional status. When the testicles are too large or too small, it may indicate abnormal development and should be promptly checked and treated in the hospital. Small testicles can be seen in external injury, dysplasia, microcephaly, congenital cryptorchidism, etc. Testicular atrophy may occur as the disease progresses. Diseases such as orchitis and testicular tumor may lead to oversized testicles, often accompanied by other uncomfortable symptoms, such as swelling and pain, and redness of scrotal skin, etc., which should be seen promptly. In addition, the size and height position of the testicles on both sides are not exactly the same, there are also certain differences, if the difference is not very big, most of them are normal cases. If the difference between the testicles on both sides is large, it is necessary to consider that it may be a disease that causes one side of the testicle to be atrophied or enlarged, such as unilateral cryptorchidism, inflammation of the testicle or epididymis, testicular syringomyelia and other diseases, and ultrasound examination can be done at the urology department of the hospital to help determine the cause.