It is not normal for a newborn baby boy to have a large and small testicle, because under normal circumstances both testicles should be completely symmetrical, the size, shape and position should be symmetrical and consistent, if there is a large and small testicle, it is likely that there is a lesion, the possible causes are as follows: First, it is more common that there may be a syringomyelia, the testicle on one side of the syringomyelia feels very large, the contents of the scrotum are relatively larger than the opposite side. The testicles are larger than normal and the contents of the scrotum are relatively larger than the opposite side, and there is a hard lump inside the scrotum when you feel it, and it is clear from the ultrasound that it is caused by testicular syringomyelia. The inflamed side is larger than the opposite side. Therefore, if the testicle is one big and one small, no matter if it is a newborn or normal, it means that there is a problem with the testicle, so you must seek medical attention in time to determine which cause it belongs to, if it is a syringomyelia, it is relatively okay, if it is inflammation or tumor, you must operate in time to remove the lesion in time to avoid serious consequences.