A safety shield system for a needle cannula (34) of a pen needle injector (20) or a similar device, wherein the safety shield may be retracted from a first position enclosing the needle cannula to a second position wherein the end of the needle cannula (34) is exposed for injection. The improved safety shield system of this invention permits retraction of the safety shield (22) during use, but extends the shield to enclose the needle cannula (34) in a locked position following use. Where the safety shield system of this invention is utilized with a pen needle injector (20) having a double ended needle cannula (34) mounted in a hub (40) received on the open end of the pen needle injector, the assembly can be safely disposed of by removing the safety shield assembly and the needle cannula hub assembly and storing the assembly in the cup-shaped cap (24) with the exposed end of the needle cannula safety enclosed within the cap. The cap also includes internal radial ribs (56) which prevent retraction of the shield prior to removal of the cap, thereby preventing inadvertent piercing of the cap during assembly of the safety shield assembly on the pen needle injector.
