An auto retractable safety syringe (11) is disclosed. The syringe has barrel (12) which has a hollow plunger (13) located therein. The plunger has piston means (39) associated therewith so as to be sealingly slideable within the barrel. The syringe further has a needle cartridge assembly (14) located in the barrel, the needle cartridge assembly comprising a needle (20), needle hub (21), and a housing (15, 16) therefor. The needle cartridge assembly is initially releasably engaged on the end of the plunger in a retracted state within the barrel prior to use, and is movable to and engageable with the end (25) of the barrel where the needle extends therefrom in an in-use position for performing an injection. During this time the plunger is withdrawn from engagement with the cartridge, so as to function in known manner as a plunger for taking fluid into the barrel and causing it to be injected into a patient. Subsequent to completion of the injection, the plunger is depressed further to cause the cartridge to auto retract the needle such that it is caused to retract into the hollow plunger.