A medical needle cover arrangement for a single-use syringe having a medical needle with a sharp tip, the needle being mounted on the syringe to project forwardly from a needle hub. A sleeve forming a part of a safety device is mounted on the syringe. The sleeve is arranged for axial movement with respect to the needle from an initial shielding position to a non-shielding position, the sleeve being blocked against forward movement with respect to the syringe from its initial shielding position. A soft needle cover overlies the needle with the sharp tip of the needle sealed by the cover. The rear end of the soft needle cover and the forward end of the syringe hub are profiled with complementary engaging surfaces. The cover has a step part-way between its ends, the step being engaged by an internal abutment at the forward end of the sleeve, to resist movement of the cover forwardly away from the syringe hub and so maintain a seal between the cover and hub. The part of the cover between the hub and the step may be subjected to compression to enhance the sealing effect.