Though vasectomy is considered to be a permanent form of birth control for men, approximately 1 in 2000 men conceive children, following vasectomy. There are two primary reasons for this:
Though it is uncommon, the vas deferens may reconnect themselves, following a vasectomy. This is called "recanalization" and is more common with procedures where a significant length of the tube was not removed. For best results, surgeons should remove a length of the vas, or cauterize the ends, to prevent recanalization and subsequent birth control failure.