Varicocele is the most commonly identifiable, surgically correctable lesion associated with male-factor infertility. Surgical correction of a varicocele, whether unilateral or bilateral, results in improvement not only in semen parameters but also in spontaneous and assisted pregnancy rates. Varicoceles seem to induce a number of changes in the testicular microenvironment. These alterations in temperature, hemodynamics, and reactive oxidative species and antioxidant concentrations have been demonstrated to produce deleterious effects on spermatogenesis. However, despite current knowledge in the pathophysiology of varicocele-associated male infertility, the exact mechanism--or mechanisms--by which varicoceles impair fertility remains elusive. This review examines scientific evidence regarding the pathophysiology of varicocele-associated male infertility.