An automatically shieldable blood collection set is provided. The blood collection set includes a needle assembly having a hub to which a needle cannula is fixedly attached. A safety shield is telescoped relative to the hub and the needle cannula and can be moved from a proximal position where the needle cannula is exposed to a distal position where the needle cannula is safely shielded. A spring is provided between the shield and the hub to propel the shield distally relative to the hub and into surrounding relationship with the needle cannula. A retainer is provided for releasably holding the shield in a proximal ready-to-use condition relative to the hub and the needle cannula. An actuator releases the retainer and enables the shield to be propelled by the spring. A lock may be provided for preventing inadvertent re-exposure of the needle cannula.