We have analyzed the effects of varicocele ligation on free testosterone levels, and investigated the interrelationships between free testosterone and fertility. The records were retrospectively evaluated for 42 infertile patients who underwent varicocele ligation, with serum free testosterone levels, follicle stimulating hormone (FSH), lutenizing hormone (LH), testosterone, estradiol, prolactin, ejaculated volume, sperm concentration and motility before and after surgery. Serum free testosterone levels increased from 12.97+/-4.16 to 13.59+/-3.93 pg/mL, but the difference was insignificant. The differences before and after surgery of patients in sperm concentration and motility were also insignificant. However, in free testosterone increasing group, the sperm concentration and motility increased significantly, from 4.05+/-4.35 to 7.90+/-8.19 million/mL (P=0.01) and from 30.64+/-21.87% to 41.00+/-22.00%, respectively (P=0.03). The increase in serum free testosterone level by varicocele ligation results in a significant improvement in sperm concentration and motility.