The surgical operation performed to render men sterile, or infertile. It consists of ligating, or tying, and then cutting the ductus, or VAS DEFERENS (see TESTICLE). It is quite a simple operation carried out under local anaesthesia, through a small incision or cut (or sometimes two) in the upper part of the SCROTUM. It has no effect on sexual drive or ejaculation, and does not cause impotence. It is not immediately effective so a test for the presence of sperm is usually advised after 3 months (and repeated if necessary) before advising that it is safe to assume that sterility has been achieved. Fertility can sometimes be restored by a further operation, to restore the continuity of the vas but the success rate is only about 30–60%. About 1 in 2,000 men become fertile again because of spontaneous recanalization of the two ends of the vas.