OBJECTIVE To determine whether high ligation is an effective treatment for infertile men with clinical varicocele. METHODS A randomized, controlled trial of high spermatic vein ligation was carried out. The patients were treated and observed for 3 years. METHODS Infertility treatment clinic and andrology laboratory in a hospital. METHODS Infertile men with abnormal semen analysis because of varicocele only. METHODS High ligation 1 year postrecruitment (group A) and at the beginning of the study (group B). RESULTS Among the 20 couples in group A, 2 pregnancies (10%) were achieved within the 1st year of observation period. During the year after high ligation, there were 8 pregnancies (44.4%), and during the 2nd year after high ligation, there were 4 more pregnancies (22.2%). In group B, 15 pregnancies (60%) occurred within the 1st year after operation. Three pregnancies (12%) and 1 pregnancy (4%) occurred during the 2nd and 3rd year, respectively. After operation in all patients of both groups, there was significant improvement in semen parameters, regardless of pregnancy occurrence. The difference in pregnancy rate (PR) between the operated group B and nonoperated group A during the 1st year of study was found to be highly significant. CONCLUSIONS It is concluded that in a population of infertile men presenting varicocele as the only demonstrable factor of infertility, the varicocele is clearly associated with infertility and reduced testicular function, and its correction by ligation improves sperm parameters and fertility rate. Furthermore, the highest PR in both groups occurred during the 1st year postoperation.