A retractable needle assembly for use in medical procedures, comprising: a needle assembly including a hub, a hollow needle passing through the hub and projecting from the posterior end of the hub, and a tubular sleeve having a radially directed hole therethrough connected with the anterior end of the hub; a tubular sheath having a wall with a radially directed hole therethrough, wherein the needle assembly is positioned within the tubular sheath so that it may be moved reversibly between an exposed position and a retracted position; a means for reversibly locking the needle assembly in its exposed position; a means for reversibly locking the needle assembly in its retracted position; and a means for permanently locking the needle assembly in its retracted position, said permanent locking means comprising a radially-directed peg mounted on an exterior surface of the tubular sheath so that one end of the radially-directed peg is adapted to be pushed inwardly through the hole in the wall of the tubular sheath and through the hole in the tubular sleeve, wherein said one end of the radially-directed peg may not be withdrawn through the hole in the tubular sleeve after it has been pushed through the hole in the tubular sleeve.