Abstract: A disposable safety syringe with a hypodermic needle of a type comprising a syringe body inside which a plunger is guided for sliding movement and wherein said needle is guided for movement to an away position inside the syringe body, further comprises:an engagement peg formed at the plunger end integrally therewith;a holding pad for said needle arranged to be movable within said body and provided with a seat for engagement with the peg; andan elastically yielding seal having a non-uniform thickness and being attached to the plunger end. The needle, as caught up after injection by the plunger peg engaging in a corresponding seat on the pad, is fully retracted into the syringe body and subjected to a sideways push from the seal effective to offset it and make re-use of the syringe impossible.