Varicoceles are dilated blood vessels in the scrotum. They are usually asymptomatic, although they may cause pain or a heavy sensation in the scrotum, and they may contribute to infertility. 90% of varicoceles are on the left side because of the anatomy of the left spermatic vein and the increased likelihood of valvular incompetence. The cremasteric and deferential veins are rarely involved. Diagnosis is by clinical examination. The cardinal sign is a scrotal mass that feels like a bag of worms. The precise mechanism for the harmful effect of varicocele on sperm quality or quantity is not known. Theories implicating increased pressure, temperature, oxygen deprivation, and decreased antioxidants have all been put forward. There is some evidence that a clinically palpable varicocele is associated with testicular atrophy, low sperm count, and poor sperm motility. Some of these parameters improve after surgery to the varicocele. The scientific evidence to support increased fertility, as measured by successful pregnancies after varicocelectomy, is poor No treatment is required, but surgical intervention is required to manage symptomatic varicocele. Following surgical intervention the complete resolution of the varicocele implies a favorable prognosis, although it is not clear whether surgery improves fertility.