A needle assembly includes a needle and a hub mounted to each other. The hub includes a sidewall spaced outwardly from the needle cannula and extending to a distal position between the opposed ends of the needle cannula. A housing integral with the hub defines a sidewall to partially confine a safety shield. The safety shield is slidably disposed about the needle cannula and releasably retained in a proximal position and can be moved to a distal position where the safety shield completely surrounds that portion of the needle hub projecting distally from the hub. The needle assembly includes a spring for propelling the safety shield to the distal position and a latch for releasing the safety shield from the proximal position. The latch may be passively activated by normal usage of the medical implement to which the needle assembly is mounted or alternately activated manually.