Many males that have gone through puberty have Varicocele, which means they have one testicle that is larger than the other, and it's a very common occurance. Varicocele is basically varicose veins in the scrotum, causing one testicle to become larger than the other and usually not a problem other than visual.
A Varicocele is an assortment of dilated blood vessels within the scrotum. These enlarged blood vessels cause one testicle to become larger than the other.
The symptoms of Varicocele, other than the size difference in the testicles can be a dull ache in the larger testicle, deterioration of the testicle and sometimes Varicocele leads to male infertility. Varicocele does not cause cancer, and does not effect male potency, as many men fear.
If the Varicocele, or large testicle, does not cause any symptoms or shows no sign of other symptoms during an exam, the Varicocele is best left alone.
If the Varicocele causes pain or other symptoms, the treatment is to surgically tie off the main testicle vein to the Varicocele.