One of my son's testicles is longer than the other. Should I be concerned?
You didn't mention your son's age, but I will assume he is still an infant. Generally, there is no concern if there is some variation in size. Few of us are perfectly symmetrical. However, if there is a large difference, then it is possible that one testicle is not developing properly. This should be checked out by a physician. In addition, there are two problems that can cause a person to think the testicles are a different size: varicocele and hydrocele.
A varicocele is caused by the veins in the scrotum swelling due to failed valves that causes the scrotum to swell on one side. It is a varicose vein in the scrotum instead of the leg. It happens on the left side more often than the right because of the direction of blood flow in the scrotum. Most men have discomfort or pain on the side of the scrotum that contains the varicocele. About fifteen percent of men between ages 15 and 25 get them. It is not directly dangerous, but the increased blood flow causes the testicle on that side to be too warm. Eventually, that warmth will reduce or stop that testicle's ability to produce sperm. An operation is needed to remove varicoceles.
A hydrocele is a build-up of fluid in the scrotum, causing one side to swell. It happens frequently to young boys in their first few months of life. The dropping of the testicles into the scrotal sac sometimes leaves the opening in the abdominal wall too large and it doesn't close up quickly. Often it will disappear on its own. If it doesn't a fairly simple surgical procedure will remedy the situation. Unlike varicoceles, hydroceles are not painful, but if they get overly large, they can exert pressure on the testicle and in some rare cases cause damage.