PIP: Although rare, failure of vasectomy can occur and should be avoided. Incidence of failure is put at 0-3%. Causes of failure are: 1) non-severance of vas deferens, 2) non-observance of period to sperm-free ejaculate after successful vas ligation, 3) recanalization of vas deferens after ligation, and 4) duplication of vas deferens was not recognized. The vas deferens is occasionally confused with neighboring structures especially in a bloody field. Verification of vas deferens resection should be done histologically. Spermatozoa can be found up to several months after successful vas ligation. They originate from seminal vesicle glands and vas deferens. Intraoperative injection of 5 ml. 0.9% aqueous nitrofurantoin solution in the central ductus stump results in inhibition of sperm motility and azoospermia. No coitus without contraceptive protection should be undertaken until proof of azoospermia is established. First spermiogram is done 6-8 weeks after procedure. Spontaneous recanalization may occur depending on vasectomy method. Factors in this process may be proliferation of ductus endothelium, formation of sperm granulomas, and tissue necrosis leading to reattachment of severed ends. Recanalization can be prevented by large resection (3-5 cm), electrocoagulation of stump epithelium or doubling over of ligated stumps. Spermatozoa antibodies develop in 50% of all vasectomized men. They cause permanent sterility even in successful vasectomy reversal. Duplication of testis and vas deferens is rare and an unlikely cause of vasectomy failure. Couples seeking vasectomy should be informed of possible failure and especially of pregnancy possibility without azoospermia.