A safety device for a medical injector supporting a needle projecting forwardly from the front of the injector has a tubular sleeve slidable rearwardly to expose at least the tip of a supported needle. The sleeve has a forward end for contacting an injection site and a removable cover for the needle is attached to the forward end of the sleeve. The sleeve has an external end face lying in a radial plane and having an orifice through which a needle projects when the sleeve slides rearwardly. The removable cover effects a seal to the forward end of the sleeve. Alternatively, the cover may frictionally engage the forward end of the sleeve or the cover may have a bore into which an enlargement member may be pressed so as to expand the cover within the sleeve and connect the cover to the sleeve.
