Purpose We assessed whether subclinical varicocele ligation improves fertility and/or semen parameters. Materials and Methods A total of 85 patients with a subclinical varicocele diagnosed by scrotal thermography presented with infertility. Patients were randomly assigned to groups 1 (high ligation of the internal spermatic vein) and 2 (followed without any treatment). At least 3 semen samples were obtained at study entry and 1 year later in both groups. Results The pregnancy rate in group 1 was 6.7 percent compared to 10 percent in group 2, and the difference was not statistically significant. Group 1 had significantly higher levels of sperm density and total motile sperm count at 1 year. There were no significant differences between groups 1 and 2 regarding change in seminal volume, sperm motility and abnormal sperm morphology. Conclusions Subclinical varicocelectomy has some effect on spermatogenesis but no beneficial effect on pregnancy rate.