A medical device comprising: a syringe having a barrel defining a reservoir within which a medicament may be held, the syringe having a needle affixed to the barrel and in fluid communication with the reservoir, the syringe further including a plunger rod and piston selectively movable within the reservoir along an injection stroke, the medicament being expelled from the reservoir through the needle by movement of the plunger rod and piston in the reservoir, and a safety shield system, said safety shield system comprising: a holder; a retainer defined on said holder and comprising a detent and two confrontingly oppositely disposed surfaces (242, 244), said retainer non-releasably securing a flange of the syringe barrel within said holder and permitting limited axial movement of the barrel therein and with respect thereto, the limited axial movement of the barrel being caused by movement of the plunger rod and piston to or near the end of the injection stroke; a shield coupled to said holder; a spring urging said shield towards an extended position; characterized in that said shield is axially movable with respect to said holder between an extended position, in which the needle is contained within said shield, and a retracted position, in which a part of the needle is not contained within said shield; a detent is defined on said holder; and a rib is defined on said shield and engageable with said detent to secure said shield in said extended position; said shield being initially deployed in said extended position and being movable from said extended position to said retracted position upon contact with the skin of a patient, said spring urging said shield from said retracted position to said extended position upon removal of contact with the skin of the patient, said detent and rib lockingly securing said shield in said extended position. a syringe having a barrel defining a reservoir within which a medicament may be held, the syringe having a needle affixed to the barrel and in fluid communication with the reservoir, the syringe further including a plunger rod and piston selectively movable within the reservoir along an injection stroke, the medicament being expelled from the reservoir through the needle by movement of the plunger rod and piston in the reservoir, and a safety shield system, said safety shield system comprising: a holder; a retainer defined on said holder and comprising a detent and two confrontingly oppositely disposed surfaces (242, 244), said retainer non-releasably securing a flange of the syringe barrel within said holder and permitting limited axial movement of the barrel therein and with respect thereto, the limited axial movement of the barrel being caused by movement of the plunger rod and piston to or near the end of the injection stroke; a shield coupled to said holder; a spring urging said shield towards an extended position; a holder; a retainer defined on said holder and comprising a detent and two confrontingly oppositely disposed surfaces (242, 244), said retainer non-releasably securing a flange of the syringe barrel within said holder and permitting limited axial movement of the barrel therein and with respect thereto, the limited axial movement of the barrel being caused by movement of the plunger rod and piston to or near the end of the injection stroke; a shield coupled to said holder; a spring urging said shield towards an extended position; said shield is axially movable with respect to said holder between an extended position, in which the needle is contained within said shield, and a retracted position, in which a part of the needle is not contained within said shield; a detent is defined on said holder; and a rib is defined on said shield and engageable with said detent to secure said shield in said extended position; said shield being initially deployed in said extended position and being movable from said extended position to said retracted position upon contact with the skin of a patient, said spring urging said shield from said retracted position to said extended position upon removal of contact with the skin of the patient, said detent and rib lockingly securing said shield in said extended position.