In normal men, there may be a difference in the size of the two testicles, but the difference is not much. If there is a big difference in the size of the two testicles, it may be varicocele, syringomyelia, etc. 1. Smaller testicles: Commonly, such as severe varicocele, mumps orchitis, cryptorchidism, etc., there may be a difference in the size of testicles on both sides. 2. Enlargement of testicles or scrotum: If there are diseases such as testicular syringomyelia, epididymitis, testicular tumor and so on may lead to enlargement of testicles, which may result in the situation of one large testicle and one small testicle. If there are obvious symptoms, you need to go to the hospital as soon as possible for examination. Sudden enlargement of testicles should exclude testicular tumor. If the testicle becomes small, we should look for the specific cause, such as testicular atrophy caused by varicocele, which will affect the testicular function such as endocrine function and spermatogenic function.