In a male, the testicles (also known as the testes) are the reproductive glands located behind the penis that produce the male hormone testosterone as well as sperm. A hydrocele is an atypical (abnormal) fluid-filled sac that surrounds a testicle and causes the scrotum to swell. Hydroceles are commonly found in infants and babies and will usually disappear without treatment. For men over the age of 40, an injury related to the scrotal area, or the results from an infection, are common causes of hydroceles. For most grown men, while benign, this condition will cease to exist on its own. However, it should be examined by a physician so that any other serious disorder can be ruled out.