Varicoceles are abnormally dilated testicular veins of the pampiniform plexus in the scrotum, which result in abnormal reflux of venous blood in the internal spermatic veins. Much like varicose veins of the legs or hemorrhoids, varicoceles represent an failure of the veins serving an organ. Varicoceles are more common on the left side, most likely due to the longer length of the testicular vein on that side as well as its right angle insertion into the renal vein.

Varicoceles can be found in up to 15% of the general population and most men with varicoceles will not experience symptoms or problems from their condition. However, having a varicocele can raise the risk of abnormal semen parameters, low testosterone, and testicular pain. In fact, 35% of men with primary infertility have varicoceles, and 81% of men with secondary infertility (inability to have more children after having at least one before).

Although most men with varicoceles go on to father children, there is ample evidence that varicoceles cause progressive impairment of male testicular function (both sperm production and testosterone production). It appears that surgical repair of varicoceles not only halts this decline in testicular function, but often reverses it. Up to 80% of men who undergo surgical repair of varicoceles will see improvements in their semen parameters. Recent studies, employing non-operated control groups indicate that varicocelectomy does improve pregnancy rates.