To evaluate whether or not dilation of the right testicular vein is a constant finding in animals with left varicocele and to illustrate its contribution to the detrimental effect of a left varicocele on the right testis, an experimental varicocele model was produced in 40 rats. Ten other rats had a sham operation (group A). Seven weeks after the operation, all 50 rats underwent laparotomy and dilation of both testicular veins was seen in 23 rats, which were randomly assigned to group B (n = 11) and group C (n = 12). One week later, groups A and C underwent sham ligation of the right testicular vein, whereas group B rats underwent resection of this vein. At 84 days after the initial operation, group C rats showed a significant reduction in right epididymal sperm content, motility, and fertilizing capacity, right testicular weight, and right testicular vs. intraabdominal temperature difference when compared with groups A and B. Since surgical repair of the secondary right varicocele improved all the parameters indicating the harmful consequences of the primary left varicocele on the right testis, it appears that dilation of the right testicular vein contributes to the detrimental effect of a left varicocele on the right testis.