Abstract: A pre-filled injection device having a retractable needle with a sharpened tip for penetrating the skin of a patient for administering medicinal fluids is provided. The pre-filled injection device of the present invention allows the needle to be manually retracted, thereby reducing the risk of transmission of various pathogens, most notably human immune virus (HIV), to infected personnel, due to an inadvertent needle stick. The present pre-filled injection device has a hollow housing which receives a pre-filled cartridge containing medicinal fluids. A needle retainer initially holds a needle projecting forwardly from the hollow housing. The rear end of the needle pierces the pre-filled cartridge when sufficient pressure is applied to the end of the pre-filled cartridge to advance it in the forward direction. A plunger is slidably displaceable within the housing. A latch member is operable in a latched position to prevent forward movement of the plunger.