The vas is the medical name for the tube along which the sperm travel from the testes to the penis. There are a number of different techniques which can be used to interrupt this process. Traditionally, two incisions were made under local anaesthetic and 1 cm of vas was removed from each side. Both ends were sealed. This method tended to occasionally lead to congestion at the testicular end due to a build up of pressure from the sperm and occasionally a sperm granuloma formed this is a small cyst at the blocked end of the tube. To avoid this, a different method has been developed whereby the tube to the outside is still sealed but the other end is enclosed in an envelope of body tissue which does not block the tube, thereby avoiding the congestion which was thought to lead to occasional post op pain. This is the method currently in use. This interruption in the supply of sperm prevents the sperm from joining the rest of the seminal fluid which is produced further along the tube. There is a small amount of discomfort for a matter of seconds while the anaesthetic is injected into the skin of the scrotum and around the vas (it feels similar to having local anaesthetic prior to having a tooth filling and it does not involve the testes). Occasionally, if the vas are difficult to feel it may not be possible to do the operation under local anaesthetic and a general anaesthetic would be required.